Re: [PATCH v3 1/2] x86, msr: allow rdmsr_safe_on_cpu() to schedule

Ingo Molnar
2018-03-24T08:09:54Z

* Eric Dumazet <edumazet@google.com> wrote:

> I noticed high latencies caused by a daemon periodically reading
> various MSR on all cpus. KASAN kernels would see ~10ms latencies
> simply reading one MSR. Even without KASAN, sending IPI to CPU
> in deep sleep state or blocking hard IRQ in a a long section,
> then waiting for the answer can consume hundreds of usec.
>
> Converts rdmsr_safe_on_cpu() to use a completion instead
> of busy polling.
>
> Overall daemon cpu usage was reduced by 35 %,
> and latencies caused by msr_read() disappeared.

What "daemon" is this and why is it reading MSRs?

Thanks,

Ingo