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

Thomas Gleixner
2018-03-24T10:50:28Z

On Sat, 24 Mar 2018, Ingo Molnar wrote:
> * 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?

Why? Just because it can ....