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

[Nir Soffer]

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.

> 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.

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