Re: [PATCH v14 25/25] sched: use static key for sched_clock_running

2018-07-19 Thread Pavel Tatashin
On Thu, Jul 19, 2018 at 6:49 AM Peter Zijlstra  wrote:
>
> On Tue, Jul 17, 2018 at 10:22:11PM -0400, Pavel Tatashin wrote:
> > sched_clock_running may be read every time sched_clock_cpu() is called.
> > Yet, this variable is updated only twice during boot, and never changes
> > again, therefore it is better to make it a static key.
>
> Right, so the focus was always on making the sane TSC case fast, and if
> TSC isn't stable we'd just make do and not care too much.
>

True for CONFIG_HAVE_UNSTABLE_SCHED_CLOCK, but for other systems like
SPARC, it hurts to have this variable accessed every time, even though
they have a sane sched_clock().

> But this certainly isn't wrong, so ACK.

Thank you,
Pave


Re: [PATCH v14 25/25] sched: use static key for sched_clock_running

2018-07-19 Thread Peter Zijlstra
On Tue, Jul 17, 2018 at 10:22:11PM -0400, Pavel Tatashin wrote:
> sched_clock_running may be read every time sched_clock_cpu() is called.
> Yet, this variable is updated only twice during boot, and never changes
> again, therefore it is better to make it a static key.

Right, so the focus was always on making the sane TSC case fast, and if
TSC isn't stable we'd just make do and not care too much.

But this certainly isn't wrong, so ACK.