From: "Simon Grinberg" <simon(a)redhat.com&gt; To: "Greg Padgett" <gpadgett(a)redhat.com&gt; Cc: "engine-devel" <engine-devel(a)ovirt.org&gt; Sent: Monday, December 17, 2012 1:13:03 PM Subject: Re: [Engine-devel] CPU Overcommit Feature ----- Original Message ----- > From: "Greg Padgett" <gpadgett(a)redhat.com&gt; > To: "engine-devel" <engine-devel(a)ovirt.org&gt; > Sent: Monday, December 17, 2012 4:37:57 PM > Subject: [Engine-devel] CPU Overcommit Feature > > Hi, > > I've been working on a feature to allow CPU Overcommitment of hosts > in a > cluster. This first stage allows the engine to consider host cpu > threads > as cores for the purposes of VM resource allocation. > > This wiki page has further details, your comments are welcome! > http://www.ovirt.org/Features/cpu_overcommit Basically looking good. Hyperthread though is vendor specific. For AMD it's Clustered Multi-Thread while for Intel it's Hyper-Thread Official name is simultaneous multithreading (SMT) but no one outside of the academy will recognize that. in libvirt if I read it right it's <attribute name='thread_siblings'> So why not just call it threads. We'll have cpuSockets, cpiCores, and cpuThreads, should be clear when in CPU context. In the GUI just change hyperthreads to CPU threads. While in the tool tip explain that it's either AMD Clustered Multi-Thread or Intel Hyperthread > > Thanks in advance, > Greg > _______________________________________________ > Engine-devel mailing list > Engine-devel(a)ovirt.org > http://lists.ovirt.org/mailman/listinfo/engine-devel > _______________________________________________ Engine-devel mailing list Engine-devel(a)ovirt.org http://lists.ovirt.org/mailman/listinfo/engine-devel

----- Original Message ----- > From: "Greg Padgett" <gpadgett(a)redhat.com&gt; > To: "engine-devel" <engine-devel(a)ovirt.org&gt; > Sent: Monday, December 17, 2012 4:37:57 PM > Subject: [Engine-devel] CPU Overcommit Feature > > Hi, > > I've been working on a feature to allow CPU Overcommitment of hosts > in a > cluster. This first stage allows the engine to consider host cpu > threads > as cores for the purposes of VM resource allocation. > > This wiki page has further details, your comments are welcome! > http://www.ovirt.org/Features/cpu_overcommit Basically looking good. Hyperthread though is vendor specific. For AMD it's Clustered Multi-Thread while for Intel it's Hyper-Thread Official name is simultaneous multithreading (SMT) but no one outside of the academy will recognize that. in libvirt if I read it right it's <attribute name='thread_siblings'> So why not just call it threads. We'll have cpuSockets, cpiCores, and cpuThreads, should be clear when in CPU context. In the GUI just change hyperthreads to CPU threads. While in the tool tip explain that it's either AMD Clustered Multi-Thread or Intel Hyperthread

----- Original Message ----- > From: "Dennis Jacobfeuerborn" <dennisml(a)conversis.de&gt; > To: engine-devel(a)ovirt.org > Sent: Tuesday, December 18, 2012 12:30:34 PM > Subject: Re: [Engine-devel] CPU Overcommit Feature > > On 12/17/2012 07:13 PM, Simon Grinberg wrote: >> >> >> ----- Original Message ----- >>> From: "Greg Padgett" <gpadgett(a)redhat.com&gt; >>> To: "engine-devel" <engine-devel(a)ovirt.org&gt; >>> Sent: Monday, December 17, 2012 4:37:57 PM >>> Subject: [Engine-devel] CPU Overcommit Feature >>> >>> Hi, >>> >>> I've been working on a feature to allow CPU Overcommitment of >>> hosts >>> in a >>> cluster. This first stage allows the engine to consider host cpu >>> threads >>> as cores for the purposes of VM resource allocation. >>> >>> This wiki page has further details, your comments are welcome! >>> http://www.ovirt.org/Features/cpu_overcommit >> >> Basically looking good. >> Hyperthread though is vendor specific. >> >> For AMD it's Clustered Multi-Thread while for Intel it's >> Hyper-Thread >> Official name is simultaneous multithreading (SMT) but no one >> outside of the academy will recognize that. >> >> in libvirt if I read it right it's <attribute >> name='thread_siblings'> >> >> So why not just call it threads. >> We'll have cpuSockets, cpiCores, and cpuThreads, should be clear >> when in CPU context. >> >> In the GUI just change hyperthreads to CPU threads. While in the >> tool tip explain that it's either AMD Clustered Multi-Thread or >> Intel Hyperthread > > Does this affect only the number of potential vCpus for the guests or > does > this also have an impact on the actual scheduling? > So far I always disabled HT out of fear that a 2 vCpu guest might > actually > be scheduled to run in 2 threads of the same core but now I'm not so > sure > anymore. In the HT case does KVM know that two threads belong to the > same > core and will it only schedule its vCpus on distinct cores? Is there > some > documentation about this somewhere? This is about the maximum number of vCPUs we can give to a VM. If the machine has 32 Physical cores that are hyperthreaded then do we say the max number of vCPUs for a single VM is 32 or 64.

----- Original Message ----- > From: "Dennis Jacobfeuerborn" <dennisml(a)conversis.de&gt; > To: "Andrew Cathrow" <acathrow(a)redhat.com&gt; > Cc: engine-devel(a)ovirt.org > Sent: Tuesday, December 18, 2012 7:59:26 PM > Subject: Re: [Engine-devel] CPU Overcommit Feature > > On 12/18/2012 06:33 PM, Andrew Cathrow wrote: >> >> >> ----- Original Message ----- >>> From: "Dennis Jacobfeuerborn" <dennisml(a)conversis.de&gt; >>> To: engine-devel(a)ovirt.org >>> Sent: Tuesday, December 18, 2012 12:30:34 PM >>> Subject: Re: [Engine-devel] CPU Overcommit Feature >>> >>> On 12/17/2012 07:13 PM, Simon Grinberg wrote: >>>> >>>> >>>> ----- Original Message ----- >>>>> From: "Greg Padgett" <gpadgett(a)redhat.com&gt; >>>>> To: "engine-devel" <engine-devel(a)ovirt.org&gt; >>>>> Sent: Monday, December 17, 2012 4:37:57 PM >>>>> Subject: [Engine-devel] CPU Overcommit Feature >>>>> >>>>> Hi, >>>>> >>>>> I've been working on a feature to allow CPU Overcommitment of >>>>> hosts >>>>> in a >>>>> cluster. This first stage allows the engine to consider host >>>>> cpu >>>>> threads >>>>> as cores for the purposes of VM resource allocation. >>>>> >>>>> This wiki page has further details, your comments are welcome! >>>>> http://www.ovirt.org/Features/cpu_overcommit >>>> >>>> Basically looking good. >>>> Hyperthread though is vendor specific. >>>> >>>> For AMD it's Clustered Multi-Thread while for Intel it's >>>> Hyper-Thread >>>> Official name is simultaneous multithreading (SMT) but no one >>>> outside of the academy will recognize that. >>>> >>>> in libvirt if I read it right it's <attribute >>>> name='thread_siblings'> >>>> >>>> So why not just call it threads. >>>> We'll have cpuSockets, cpiCores, and cpuThreads, should be clear >>>> when in CPU context. >>>> >>>> In the GUI just change hyperthreads to CPU threads. While in the >>>> tool tip explain that it's either AMD Clustered Multi-Thread or >>>> Intel Hyperthread >>> >>> Does this affect only the number of potential vCpus for the guests >>> or >>> does >>> this also have an impact on the actual scheduling? >>> So far I always disabled HT out of fear that a 2 vCpu guest might >>> actually >>> be scheduled to run in 2 threads of the same core but now I'm not >>> so >>> sure >>> anymore. In the HT case does KVM know that two threads belong to >>> the >>> same >>> core and will it only schedule its vCpus on distinct cores? Is >>> there >>> some >>> documentation about this somewhere? >> >> This is about the maximum number of vCPUs we can give to a VM. >> If the machine has 32 Physical cores that are hyperthreaded then do >> we say the max number of vCPUs for a single VM is 32 or 64. > > If the actual scheduling of vCPUs cannot distinguish between threads > and > cores then why would you even want to limit yourself to 32 in you > example? > In that case the scheduling might end up being inefficient no matter > how > many vCPUs you assign to a guest so why restrict the user? (You might > of > course want to limit the user for policy reasons but that has nothing > to to > with the thread/core topic.) > > On the other hand if KVM does only schedule the vCPUs on distinct > cores and > extending the count from 32 to 64 implies that this distinction is to > be > disabled then this will have a performance impact for the guest. > In that case I might want to limit the guests to just the 32 physical > cores > so two vCPUs of a single guest don't get scheduled on two threads of > the > same core. > > I've never really looked that closely into the scheduling issue but > it > might play a role here so I asked if someone had any pointers to > infos > about how exactly KVM makes its scheduling decisions. > > Regards, > Dennis > Dennis, first of all every virtual cpu is basically a qemu-thread which can run on any cpu-thread. The scheduling is done by the kernel scheduler, while we may control it using cpu pinning. ie- you may ask for specific vcpu to run on a specific thread which is from the OS point of view another core. Indeed there are cases where this is not recommended, but other cases where this will actually give you a performance boost, as L1 cache is being shared by the sibling threads. So it's really up to you to test your workload and decide id you wish to utilize it or not. We're giving you powerful tools, and you can decide if and how to use it.

Hi, I've been working on a feature to allow CPU Overcommitment of hosts in a cluster. This first stage allows the engine to consider host cpu threads as cores for the purposes of VM resource allocation. This wiki page has further details, your comments are welcome! http://www.ovirt.org/Features/cpu_overcommit

----- Original Message ----- > From: "Dan Kenigsberg" <danken(a)redhat.com&gt; > To: "Greg Padgett" <gpadgett(a)redhat.com&gt; > Cc: "engine-devel" <engine-devel(a)ovirt.org&gt;, vdsm-devel(a)fedorahosted.org > Sent: Wednesday, December 19, 2012 3:59:11 PM > Subject: Re: [Engine-devel] CPU Overcommit Feature > > On Mon, Dec 17, 2012 at 09:37:57AM -0500, Greg Padgett wrote: > > Hi, > > > > I've been working on a feature to allow CPU Overcommitment of hosts > > in a cluster. This first stage allows the engine to consider host > > cpu threads as cores for the purposes of VM resource allocation. > > > > This wiki page has further details, your comments are welcome! > > http://www.ovirt.org/Features/cpu_overcommit > > I've commented about the vdsm/engine API on > http://gerrit.ovirt.org/#/c/10144/ but it is probably better to > reiterate it here. > > The suggested API is tightly coupled with an ugly hack we pushed to > vdsm > in order not to solve the issue properly on the first strike. > > If we had not have report_host_threads_as_cores, I think we'd have a > simpler API reporting only cpuThreads and cpuCores; with no funny > boolean flags. > > Let us strive to that position as much as we can. > > How about asking whoever used report_host_threads_as_cores to unset > it > once they install Engine 3.2 ? I think that these are very few > people, > that would not mind this very much. > > If this is impossible, I'd add a cpuCores2, always reporting the true > number, to be used by new Engines. We may even report it only on the > very few cases of report_host_threads_as_cores being set. > > Dan. Hi Dan, Thanks for the review. I agree simply reporting cores and threads would be the right solution. However, when you have hyperthreading turned off you get cores=threads. This is the same situation you have when hyperthreading turned on, and someone used the vdsm configuration of reporting threads as cores. So the engine won't know the real status of the host.

We need to be able to tell the difference. So this moves us to cpuCores2 suggestion. This is one possibility (cpuRealCores?), and the alternative is an indication of vdsm config (true/false) which may be removed in the future. I suspect over time cpu and cpu2 will confuse people. So I'd suggest having the boolean and removing it along with the vdsm configuration in the next ovirt version.

On 12/20/2012 09:43 AM, Dan Kenigsberg wrote: >On Wed, Dec 19, 2012 at 09:53:15AM -0500, Doron Fediuck wrote: >> >>----- Original Message ----- >>>From: "Dan Kenigsberg" <danken(a)redhat.com&gt; >>>To: "Greg Padgett" <gpadgett(a)redhat.com&gt; >>>Cc: "engine-devel" <engine-devel(a)ovirt.org&gt;, vdsm-devel(a)fedorahosted.org >>>Sent: Wednesday, December 19, 2012 3:59:11 PM >>>Subject: Re: [Engine-devel] CPU Overcommit Feature >>> >>>On Mon, Dec 17, 2012 at 09:37:57AM -0500, Greg Padgett wrote: >>>>Hi, >>>> >>>>I've been working on a feature to allow CPU Overcommitment of hosts >>>>in a cluster. This first stage allows the engine to consider host >>>>cpu threads as cores for the purposes of VM resource allocation. >>>> >>>>This wiki page has further details, your comments are welcome! >>>>http://www.ovirt.org/Features/cpu_overcommit >>> >>>I've commented about the vdsm/engine API on >>>http://gerrit.ovirt.org/#/c/10144/ but it is probably better to >>>reiterate it here. >>> >>>The suggested API is tightly coupled with an ugly hack we pushed to >>>vdsm >>>in order not to solve the issue properly on the first strike. >>> >>>If we had not have report_host_threads_as_cores, I think we'd have a >>>simpler API reporting only cpuThreads and cpuCores; with no funny >>>boolean flags. >>> >>>Let us strive to that position as much as we can. >>> >>>How about asking whoever used report_host_threads_as_cores to unset >>>it >>>once they install Engine 3.2 ? I think that these are very few >>>people, >>>that would not mind this very much. >>> >>>If this is impossible, I'd add a cpuCores2, always reporting the true >>>number, to be used by new Engines. We may even report it only on the >>>very few cases of report_host_threads_as_cores being set. >>> >>>Dan. >> >>Hi Dan, >>Thanks for the review. >> >>I agree simply reporting cores and threads would be the right solution. >>However, when you have hyperthreading turned off you get cores=threads. >>This is the same situation you have when hyperthreading turned on, and >>someone used the vdsm configuration of reporting threads as cores. >> >>So the engine won't know the real status of the host. > >This is not surprising, as report_host_threads_as_cores means in blunt >English "lie to Engine about the number of cores". The newly suggested >flag says "don't believe what I said in cpuCores, since I'm lying". Next >thing we'd have is another flag saying that the former flag was a lie, >and cpuCores is actually trustworthy. > >Instead of dancing this dance, I suggest to stop lying. > >report_host_threads_as_cores was a hack to assist a older Engine >versions. Engine users that needed it had to set it out-of-band on their >hosts. Now if they upgrade their Engine, they can -- as easily -- reset >that value. > >If they forget, nothing devastating happens beyond Engine assuming that >hyperthreading is off. > >Please consider this suggestion. I find it the simplest for all involved >parties. the only problem is the new vdsm doesn't know which engine may be using it. if engine would say "getVdsCaps engineVersion=3.2", then vdsm could know engine no longer needs lying to and ignore the flag, re-using same field.

From: "Doron Fediuck" <dfediuck(a)redhat.com&gt; To: "Dan Kenigsberg" <danken(a)redhat.com&gt; Cc: "engine-devel" <engine-devel(a)ovirt.org&gt;, vdsm-devel(a)fedorahosted.org Sent: Thursday, December 20, 2012 2:14:45 PM Subject: Re: [Engine-devel] [vdsm] CPU Overcommit Feature ----- Original Message ----- > From: "Dan Kenigsberg" <danken(a)redhat.com&gt; > To: "Itamar Heim" <iheim(a)redhat.com&gt; > Cc: "engine-devel" <engine-devel(a)ovirt.org&gt;, > vdsm-devel(a)fedorahosted.org > Sent: Thursday, December 20, 2012 11:55:10 AM > Subject: Re: [Engine-devel] [vdsm] CPU Overcommit Feature > > On Thu, Dec 20, 2012 at 10:23:55AM +0200, Itamar Heim wrote: > > On 12/20/2012 09:43 AM, Dan Kenigsberg wrote: > > >On Wed, Dec 19, 2012 at 09:53:15AM -0500, Doron Fediuck wrote: > > >> > > >>----- Original Message ----- > > >>>From: "Dan Kenigsberg" <danken(a)redhat.com&gt; > > >>>To: "Greg Padgett" <gpadgett(a)redhat.com&gt; > > >>>Cc: "engine-devel" <engine-devel(a)ovirt.org&gt;, > > &gt;&gt;&gt;vdsm-devel(a)fedorahosted.org > > >>>Sent: Wednesday, December 19, 2012 3:59:11 PM > > >>>Subject: Re: [Engine-devel] CPU Overcommit Feature > > >>> > > >>>On Mon, Dec 17, 2012 at 09:37:57AM -0500, Greg Padgett wrote: > > >>>>Hi, > > >>>> > > >>>>I've been working on a feature to allow CPU Overcommitment of > > >>>>hosts > > >>>>in a cluster. This first stage allows the engine to consider > > >>>>host > > >>>>cpu threads as cores for the purposes of VM resource > > >>>>allocation. > > >>>> > > >>>>This wiki page has further details, your comments are > > >>>>welcome! > > >>>>http://www.ovirt.org/Features/cpu_overcommit > > >>> > > >>>I've commented about the vdsm/engine API on > > >>>http://gerrit.ovirt.org/#/c/10144/ but it is probably better > > >>>to > > >>>reiterate it here. > > >>> > > >>>The suggested API is tightly coupled with an ugly hack we > > >>>pushed > > >>>to > > >>>vdsm > > >>>in order not to solve the issue properly on the first strike. > > >>> > > >>>If we had not have report_host_threads_as_cores, I think we'd > > >>>have a > > >>>simpler API reporting only cpuThreads and cpuCores; with no > > >>>funny > > >>>boolean flags. > > >>> > > >>>Let us strive to that position as much as we can. > > >>> > > >>>How about asking whoever used report_host_threads_as_cores to > > >>>unset > > >>>it > > >>>once they install Engine 3.2 ? I think that these are very few > > >>>people, > > >>>that would not mind this very much. > > >>> > > >>>If this is impossible, I'd add a cpuCores2, always reporting > > >>>the > > >>>true > > >>>number, to be used by new Engines. We may even report it only > > >>>on > > >>>the > > >>>very few cases of report_host_threads_as_cores being set. > > >>> > > >>>Dan. > > >> > > >>Hi Dan, > > >>Thanks for the review. > > >> > > >>I agree simply reporting cores and threads would be the right > > >>solution. > > >>However, when you have hyperthreading turned off you get > > >>cores=threads. > > >>This is the same situation you have when hyperthreading turned > > >>on, and > > >>someone used the vdsm configuration of reporting threads as > > >>cores. > > >> > > >>So the engine won't know the real status of the host. > > > > > >This is not surprising, as report_host_threads_as_cores means in > > >blunt > > >English "lie to Engine about the number of cores". The newly > > >suggested > > >flag says "don't believe what I said in cpuCores, since I'm > > >lying". Next > > >thing we'd have is another flag saying that the former flag was > > >a > > >lie, > > >and cpuCores is actually trustworthy. > > > > > >Instead of dancing this dance, I suggest to stop lying. > > > > > >report_host_threads_as_cores was a hack to assist a older Engine > > >versions. Engine users that needed it had to set it out-of-band > > >on > > >their > > >hosts. Now if they upgrade their Engine, they can -- as easily > > >-- > > >reset > > >that value. > > > > > >If they forget, nothing devastating happens beyond Engine > > >assuming > > >that > > >hyperthreading is off. > > > > > >Please consider this suggestion. I find it the simplest for all > > >involved > > >parties. > > > > the only problem is the new vdsm doesn't know which engine may be > > using it. > > if engine would say "getVdsCaps engineVersion=3.2", then vdsm > > could > > know engine no longer needs lying to and ignore the flag, > > re-using > > same field. > > Note that I do not suggest to drop report_host_threads_as_cores > now. > I am suggesting to keep on lying even to new Engine. > If someone thinks that lying is bad, he should reset > report_host_threads_as_cores. > > It seems to me that the suggested API is being coerced by a very > limited > use case, that is not going to be really harmed by a > straight-forward > API. > > Dan. Dan, Did some further checking, and we can go with it; So basically now we add cpuThreads. Additionally, if the report_host_threads_as_cores is turned on, an additional cpuCoresReal will be reported.

Since this is a 3.2 cluster feature, the engine will make sure to update the DB with the real numbers, and older clusters will use the information vdsm reports, while blocking the engine side optimization. An update path is already available here: http://gerrit.ovirt.org/#/c/10144/4 I hope that for cluster 3.3 we'll be able to drop the vdsm configuration. A review would be highly appreciated due to the holidays proximity. Doron _______________________________________________ Engine-devel mailing list Engine-devel(a)ovirt.org http://lists.ovirt.org/mailman/listinfo/engine-devel

----- Original Message ----- > From: "Simon Grinberg" <simon(a)redhat.com&gt; > To: "Doron Fediuck" <dfediuck(a)redhat.com&gt; > Cc: "engine-devel" <engine-devel(a)ovirt.org&gt;, vdsm-devel(a)fedorahosted.org > Sent: Thursday, December 20, 2012 4:56:14 PM > Subject: Re: [Engine-devel] [vdsm] CPU Overcommit Feature > > > > ----- Original Message ----- > > From: "Doron Fediuck" <dfediuck(a)redhat.com&gt; > > To: "Dan Kenigsberg" <danken(a)redhat.com&gt; > > Cc: "engine-devel" <engine-devel(a)ovirt.org&gt;, > > vdsm-devel(a)fedorahosted.org > > Sent: Thursday, December 20, 2012 2:14:45 PM > > Subject: Re: [Engine-devel] [vdsm] CPU Overcommit Feature > > > > > > > > ----- Original Message ----- > > > From: "Dan Kenigsberg" <danken(a)redhat.com&gt; > > > To: "Itamar Heim" <iheim(a)redhat.com&gt; > > > Cc: "engine-devel" <engine-devel(a)ovirt.org&gt;, > > > vdsm-devel(a)fedorahosted.org > > > Sent: Thursday, December 20, 2012 11:55:10 AM > > > Subject: Re: [Engine-devel] [vdsm] CPU Overcommit Feature > > > > > > On Thu, Dec 20, 2012 at 10:23:55AM +0200, Itamar Heim wrote: > > > > On 12/20/2012 09:43 AM, Dan Kenigsberg wrote: > > > > >On Wed, Dec 19, 2012 at 09:53:15AM -0500, Doron Fediuck wrote: > > > > >> > > > > >>----- Original Message ----- > > > > >>>From: "Dan Kenigsberg" <danken(a)redhat.com&gt; > > > > >>>To: "Greg Padgett" <gpadgett(a)redhat.com&gt; > > > > >>>Cc: "engine-devel" <engine-devel(a)ovirt.org&gt;, > > > > &gt;&gt;&gt;vdsm-devel(a)fedorahosted.org > > > > >>>Sent: Wednesday, December 19, 2012 3:59:11 PM > > > > >>>Subject: Re: [Engine-devel] CPU Overcommit Feature > > > > >>> > > > > >>>On Mon, Dec 17, 2012 at 09:37:57AM -0500, Greg Padgett > > > > >>>wrote: > > > > >>>>Hi, > > > > >>>> > > > > >>>>I've been working on a feature to allow CPU Overcommitment > > > > >>>>of > > > > >>>>hosts > > > > >>>>in a cluster. This first stage allows the engine to > > > > >>>>consider > > > > >>>>host > > > > >>>>cpu threads as cores for the purposes of VM resource > > > > >>>>allocation. > > > > >>>> > > > > >>>>This wiki page has further details, your comments are > > > > >>>>welcome! > > > > >>>>http://www.ovirt.org/Features/cpu_overcommit > > > > >>> > > > > >>>I've commented about the vdsm/engine API on > > > > >>>http://gerrit.ovirt.org/#/c/10144/ but it is probably better > > > > >>>to > > > > >>>reiterate it here. > > > > >>> > > > > >>>The suggested API is tightly coupled with an ugly hack we > > > > >>>pushed > > > > >>>to > > > > >>>vdsm > > > > >>>in order not to solve the issue properly on the first > > > > >>>strike. > > > > >>> > > > > >>>If we had not have report_host_threads_as_cores, I think > > > > >>>we'd > > > > >>>have a > > > > >>>simpler API reporting only cpuThreads and cpuCores; with no > > > > >>>funny > > > > >>>boolean flags. > > > > >>> > > > > >>>Let us strive to that position as much as we can. > > > > >>> > > > > >>>How about asking whoever used report_host_threads_as_cores > > > > >>>to > > > > >>>unset > > > > >>>it > > > > >>>once they install Engine 3.2 ? I think that these are very > > > > >>>few > > > > >>>people, > > > > >>>that would not mind this very much. > > > > >>> > > > > >>>If this is impossible, I'd add a cpuCores2, always reporting > > > > >>>the > > > > >>>true > > > > >>>number, to be used by new Engines. We may even report it > > > > >>>only > > > > >>>on > > > > >>>the > > > > >>>very few cases of report_host_threads_as_cores being set. > > > > >>> > > > > >>>Dan. > > > > >> > > > > >>Hi Dan, > > > > >>Thanks for the review. > > > > >> > > > > >>I agree simply reporting cores and threads would be the right > > > > >>solution. > > > > >>However, when you have hyperthreading turned off you get > > > > >>cores=threads. > > > > >>This is the same situation you have when hyperthreading > > > > >>turned > > > > >>on, and > > > > >>someone used the vdsm configuration of reporting threads as > > > > >>cores. > > > > >> > > > > >>So the engine won't know the real status of the host. > > > > > > > > > >This is not surprising, as report_host_threads_as_cores means > > > > >in > > > > >blunt > > > > >English "lie to Engine about the number of cores". The newly > > > > >suggested > > > > >flag says "don't believe what I said in cpuCores, since I'm > > > > >lying". Next > > > > >thing we'd have is another flag saying that the former flag > > > > >was > > > > >a > > > > >lie, > > > > >and cpuCores is actually trustworthy. > > > > > > > > > >Instead of dancing this dance, I suggest to stop lying. > > > > > > > > > >report_host_threads_as_cores was a hack to assist a older > > > > >Engine > > > > >versions. Engine users that needed it had to set it > > > > >out-of-band > > > > >on > > > > >their > > > > >hosts. Now if they upgrade their Engine, they can -- as easily > > > > >-- > > > > >reset > > > > >that value. > > > > > > > > > >If they forget, nothing devastating happens beyond Engine > > > > >assuming > > > > >that > > > > >hyperthreading is off. > > > > > > > > > >Please consider this suggestion. I find it the simplest for > > > > >all > > > > >involved > > > > >parties. > > > > > > > > the only problem is the new vdsm doesn't know which engine may > > > > be > > > > using it. > > > > if engine would say "getVdsCaps engineVersion=3.2", then vdsm > > > > could > > > > know engine no longer needs lying to and ignore the flag, > > > > re-using > > > > same field. > > > > > > Note that I do not suggest to drop report_host_threads_as_cores > > > now. > > > I am suggesting to keep on lying even to new Engine. > > > If someone thinks that lying is bad, he should reset > > > report_host_threads_as_cores. > > > > > > It seems to me that the suggested API is being coerced by a very > > > limited > > > use case, that is not going to be really harmed by a > > > straight-forward > > > API. > > > > > > Dan. > > > > Dan, > > Did some further checking, and we can go with it; > > So basically now we add cpuThreads. Additionally, if the > > report_host_threads_as_cores > > is turned on, an additional cpuCoresReal will be reported. > > No need for that. > There is only one problematic state where VDSM cheats and reports > cores == threads. > This does not happen by mistake, the user specifically asked for it. > > The above condition above also happens if threads is really off or > the processor does not have threads, so it's a state we need to > handle in any case. > > So just report threads=off, whenever cores == threads and treat it as > such. If the user is unhappy then he should just turn off the cheat > mode. > ack. * <3.2 clusters are not supported. * >=3.2 clusters will assume HT off unless cores < threads. Some release note is needed for this, so users will be advised to turn off vdsm cheating when upgrading to new 3.2 engine, in case they happen to use it.