On Sun, Nov 29, 2015 at 6:01 PM, Yaniv Kaul <ykaul@redhat.com> wrote:
> On Sun, Nov 29, 2015 at 5:37 PM, Nir Soffer <nsoffer@redhat.com> wrote:
>>
>> On Sun, Nov 29, 2015 at 10:37 AM, Yaniv Kaul <ykaul@redhat.com> wrote:
>> >
>> > On Fri, Nov 27, 2015 at 6:55 PM, Francesco Romani <fromani@redhat.com>
>> > wrote:
>> >>
>> >> Using taskset, the ip command now takes a little longer to complete.
>> >
>> >
>> > Since we always use the same set of CPUs, I assume using a mask (for 0 &
>> > 1,
>> > just use 0x3, as the man suggests) might be a tiny of a fraction faster
>> > to
>> > execute taskset with, instead of the need to translate the numeric CPU
>> > list.
>>
>> Creating the string "0-<last cpu index>" is one line in vdsm. The code
>> handling this in
>> taskset is written in C, so the parsing time is practically zero. Even
>> if it was non-zero,
>> this code run once when we run a child process, so the cost is
>> insignificant.
>
>
> I think it's easier to just to have it as a mask in a config item somewhere,
> without need to create it or parse it anywhere.
> For us and for the user.

We have this option in /etc/vdsm/vdsm.conf:

I think this is the easiest option for users.

>> > However, the real concern is making sure CPUs 0 & 1 are not really too
>> > busy
>> > with stuff (including interrupt handling, etc.)
>>
>> This code is used when we run a child process, to allow the child
>> process to run on
>> all cpus (in this case, cpu 0 and cpu 1). So I think there is no concern
>> here.
>>
>> Vdsm itself is running by default on cpu 1, which should be less busy
>> then cpu 0.
>
>
> I assume those are cores, which probably in a multi-socket will be in the
> first socket only.
> There's a good chance that the FC and or network/cards will also bind their
> interrupts to core0 & core 1 (check /proc/interrupts) on the same socket.
> From my poor laptop (1s, 4c):
> 42:    1487104       9329       4042       3598  IR-PCI-MSI 512000-edge    
> 0000:00:1f.2
>
> (my SATA controller)
>
> 43:   14664923         34         18         13  IR-PCI-MSI 327680-edge    
> xhci_hcd
> (my dock station connector)
>
> 45:    6754579       4437       2501       2419  IR-PCI-MSI 32768-edge    
> i915
> (GPU)
>
> 47:     187409      11627       1235       1259  IR-PCI-MSI 2097152-edge    
> iwlwifi
> (NIC, wifi)

Interesting, here an example from a 8 cores machine running my vms: