Re: [Engine-devel] CPU Pinning @engine

On 21/05/12 11:16, Yaniv Kaul wrote: > On 05/21/2012 11:08 AM, Doron Fediuck wrote: >> On 21/05/12 11:01, Dor Laor wrote: >>> On 05/21/2012 10:58 AM, Doron Fediuck wrote: >>>> On 21/05/12 01:45, Andrew Cathrow wrote: >>>>> ----- Original Message ----- >>>>>> From: "Doron Fediuck"<dfediuck(a)redhat.com> >>>>>> To: dlaor(a)redhat.com >>>>>> Cc: engine-devel(a)ovirt.org >>>>>> Sent: Sunday, May 20, 2012 5:49:08 PM >>>>>> Subject: Re: [Engine-devel] CPU Pinning @engine >>>>>> >>>>>> On 20/05/12 21:41, Dor Laor wrote: >>>>>>> On 05/17/2012 11:15 PM, Doron Fediuck wrote: >>>>>>>> On 17/05/12 20:28, Ayal Baron wrote: >>>>>>>>> "Live migration will not be supported for such VM's." >>>>>>>>> >>>>>>>>> Migration will work on homogeneous clusters so this should not be >>>>>>>>> enforced (not limited to VMs which are pinned to host) just give >>>>>>>>> a warning. >>>>>>>>> >>>>>>>> I agree, but if we wish to ping vCPUx to pCPUy in host a, we >>>>>>>> cannot ensure to have the same in host b, >>>>>>>> since it may have pCPUy too busy, so performance will degrade. >>>>>>>> Also, I hope you saw my general comment >>>>>>> Performance may degrade on any migration to loaded host regardless >>>>>>> of pinning. >>>>>>> >>>>>>> There is not need to forbid migration. Instead, the SLA assurance >>>>>>> policy should verify the dedicated resources and match the target >>>>>>> w/ the guarantee and decide according to this. >>>>>>> >>>>>> Thanks for the input. >>>>>> We may start with migration blocked in a configurable manner, so >>>>>> people who wish migrate to work >>>>>> will simply set the relevant configuration key. >>>>>> As for looking for a matched CPU, will add it as p2. >>>>> We shouldn't block migration >>>>> If a user wants to not migrate a cpu pinned VM then let them use the non-migratable flag in the UI. >>>>> >>>> We're not blocking migration, we're allowing pinning (for now) only for non-migrative VM's. >>>> For p2 we'll verify destination host has the relevant pinning capacity, which will allow >>>> pinning for migrative VM's as well. >>> IMHO the order should be the opposite - if the user likes to migrate a pinned VM, let him (you can pop some message if you like). >> I'll check it with UI guys (AFAIK engine UI has no pop-ups). >> Also, I prefer safe than sorry. So start with a safe working pinning for pinned-to-host VMs, and then push the envelope. > Safe is letting the user migrate. It may or may not succeed (I'd worry it may put a host into Error state - I hope we've removed this state). This is a pure speculation. If I'm pinning a specific VM to a specific host, and its vCPUS into specific pCPUs, how can live migration be considered a safe thing? If I pinned to host, this is a violation of my request. Now, let's say I didn't pin to host, but I ask for specific vCPUS pinning into specific pCPUs. For now, there's no guarantee the destination host will have a relevant CPU capacity (maybe even topology), so CPU pinning may not work, which is also a violation of my request. Is live migration really the safe thing to do here??? Why not alert me so I could manually migrate to where I think is better? Having that said, I'm reminding you the somewhere earlier in this thread I wrote we'll make the constraint of cpu pinning allowed only on pinned-to-host VMs configurable, so people who wish to walk on wild side, can give it a go.

> Sorry is when you wish you had done so initially. ;-) In this case, I disagree as this is configurable. > Y. > > >>>>>>>> about starting with a humble solution and gradually improving. In >>>>>>>> this context (auto)numa can help us, >>>>>>>> so we better do numa than handle migration for basic mode, risking >>>>>>>> performance issues. >>>>>>>> >>>>>>>>> ----- Original Message ----- >>>>>>>>>> From: "Doron Fediuck"<dfediuck(a)redhat.com> >>>>>>>>>> To: engine-devel(a)ovirt.org >>>>>>>>>> Sent: Thursday, May 17, 2012 2:42:46 PM >>>>>>>>>> Subject: [Engine-devel] CPU Pinning @engine >>>>>>>>>> >>>>>>>>>> Hi All, >>>>>>>>>> Currently the VDSM has a CPU pinning hook. >>>>>>>>>> We'd like to add better support of it into the engine itself. >>>>>>>>>> Here's a design draft to cover it: >>>>>>>>>> http://www.ovirt.org/wiki/Features/Design/cpu-pinning >>>>>>>>>> >>>>>>>>>> Please review and comment if needed. >>>>>>>>>> >>>>>>>>>> Thanks! >>>>>>>>>> -- >>>>>>>>>> >>>>>>>>>> /d >>>>>>>>>> >>>>>>>>>> Never say "OOPS!" always say "Ah, Interesting!" >>>>>>>>>> _______________________________________________ >>>>>>>>>> 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 >>>>>> -- >>>>>> >>>>>> /d >>>>>> >>>>>> Never say "OOPS!" always say "Ah, Interesting!" >>>>>> _______________________________________________ >>>>>> Engine-devel mailing list >>>>>> Engine-devel(a)ovirt.org >>>>>> http://lists.ovirt.org/mailman/listinfo/engine-devel >>>>>>