On 2/2/2022 5:07 PM, Ian Rogers wrote:
> Such a literal is useful to calculate things like the average frequency
> [1]. The TSC frequency isn't exposed by sysfs although some experimental
> drivers look to add it [2]. This change computes the value using the
> frequency in /proc/cpuinfo which is accruate at least on Intel
> processors.
FWIW the information in /proc/cpuinfo is going away.
You should really use CPUID for this, which has a new leaf for this.
Unfortunately there
were a few systems were it was inaccurate, but I suppose you could still
prefer /proc/cpuinfo
Also your method will not work when the metrics are used through perf
stat report or perf script
and run on another system. For the perf script case there is support for
putting the TSC into
perf.data (that is needed for PT), but the header is not dumped by
default unfortunately.
So likely you would need some new mechanism for that.
-Andi
On Wed, Feb 2, 2022 at 7:59 PM Andi Kleen <[email protected]> wrote:
>
>
> On 2/2/2022 5:07 PM, Ian Rogers wrote:
> > Such a literal is useful to calculate things like the average frequency
> > [1]. The TSC frequency isn't exposed by sysfs although some experimental
> > drivers look to add it [2]. This change computes the value using the
> > frequency in /proc/cpuinfo which is accruate at least on Intel
> > processors.
>
> FWIW the information in /proc/cpuinfo is going away.
>
> You should really use CPUID for this, which has a new leaf for this.
> Unfortunately there
>
> were a few systems were it was inaccurate, but I suppose you could still
> prefer /proc/cpuinfo
>
> Also your method will not work when the metrics are used through perf
> stat report or perf script
>
> and run on another system. For the perf script case there is support for
> putting the TSC into
>
> perf.data (that is needed for PT), but the header is not dumped by
> default unfortunately.
>
> So likely you would need some new mechanism for that.
Thanks Andi,
yep metrics with perf stat record are broken on a number of fronts and
this will be another that will need a fix. It looks like the cpuid
approach won't work pre-Skylake so sysfs could act as a fallback, but
I don't have an ETA on when that will be available. We could have
additional warnings when reading /proc/cpuinfo fails. Wdyt?
Thanks,
Ian
> -Andi
>