[ovirt-devel] [vdsm] strange network test failure on FC23

[Yaniv Kaul]

On Sun, Nov 29, 2015 at 5:37 PM, Nir Soffer <nsoffer at redhat.com> wrote:

> On Sun, Nov 29, 2015 at 10:37 AM, Yaniv Kaul <ykaul at redhat.com> wrote:
> >
> > On Fri, Nov 27, 2015 at 6:55 PM, Francesco Romani <fromani at 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.


> > 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)

Y.



> The user can modify this configuration on the host, I guess we need to
> expose this
> on the engine side (cluster setting?).
>
> Also if vdsm is pinned to certain cpu, should user get a warning
> trying to pin a vm
> to this cpu?
>
> Michal, what do you think?
>
> Nir
>
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