Re: [PATCH] x86: use cpufreq_quick_get() for /proc/cpuinfo "cpu MHz" again

[Linus Torvalds]

On Tue, Nov 14, 2017 at 4:04 PM, Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> On Tue, Nov 14, 2017 at 3:53 PM, Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
>> Current head + Raphaels patch:
>>
>> real    0m0.029s
>> user    0m0.000s
>> sys     0m0.010s
>>
>> So that patch is actually slower.
>
> Oh it definitely is expected to be slower, because it does the IPI to
> all the cores and actually gets their frequency right.
>
> It was the old one that we had to revert (because it did so
> sequentially) that was really bad, and took something like 2+ seconds
> on Ingo's 160-core thing, iirc.

Looked it up. Ingo's machine "only" had 120 cores, and he said

    fomalhaut:~> time cat /proc/cpuinfo  >/dev/null
    real    0m2.689s

for the bad serial case, so yeah, it looks "a bit" better than it was ;)

             Linus