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SubjectRe: x86: improve default idle

* Andrew Morton <akpm@linux-foundation.org> wrote:

> On Fri, 18 Apr 2008 17:37:02 GMT
> Linux Kernel Mailing List <linux-kernel@vger.kernel.org> wrote:
>
> > Gitweb: http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=13af4836b3914b23946f6a8982934e2c828c183f
> > Commit: 13af4836b3914b23946f6a8982934e2c828c183f
> > Parent: f5149a49f994e5c469ac398af7cdeb8eb612d3a4
> > Author: Ingo Molnar <mingo@elte.hu>
> > AuthorDate: Wed Apr 2 13:23:22 2008 +0200
> > Committer: Ingo Molnar <mingo@elte.hu>
> > CommitDate: Thu Apr 17 17:41:34 2008 +0200
> >
> > x86: improve default idle
> >
> > Signed-off-by: Ingo Molnar <mingo@elte.hu>
> > ---
> > arch/x86/kernel/process_32.c | 8 --------
> > arch/x86/kernel/process_64.c | 8 --------
> > 2 files changed, 0 insertions(+), 16 deletions(-)
> >
> > diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
> > index 08c41ed..3903a8f 100644
> > --- a/arch/x86/kernel/process_32.c
> > +++ b/arch/x86/kernel/process_32.c
> > @@ -113,16 +113,8 @@ void default_idle(void)
> >
> > local_irq_disable();
> > if (!need_resched()) {
> > - ktime_t t0, t1;
> > - u64 t0n, t1n;
> > -
> > - t0 = ktime_get();
> > - t0n = ktime_to_ns(t0);
> > safe_halt(); /* enables interrupts racelessly */
> > local_irq_disable();
> > - t1 = ktime_get();
> > - t1n = ktime_to_ns(t1);
> > - sched_clock_idle_wakeup_event(t1n - t0n);
> > }
> > local_irq_enable();
> > current_thread_info()->status |= TS_POLLING;
> > diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
> > index 4f40272..e75ccc8 100644
> > --- a/arch/x86/kernel/process_64.c
> > +++ b/arch/x86/kernel/process_64.c
> > @@ -107,16 +107,8 @@ void default_idle(void)
> > smp_mb();
> > local_irq_disable();
> > if (!need_resched()) {
> > - ktime_t t0, t1;
> > - u64 t0n, t1n;
> > -
> > - t0 = ktime_get();
> > - t0n = ktime_to_ns(t0);
> > safe_halt(); /* enables interrupts racelessly */
> > local_irq_disable();
> > - t1 = ktime_get();
> > - t1n = ktime_to_ns(t1);
> > - sched_clock_idle_wakeup_event(t1n - t0n);
> > }
> > local_irq_enable();
> > current_thread_info()->status |= TS_POLLING;
>
> Ingo, what's going on? There is no way that this patch is so obvious
> that it doesn't even need a changelog.

sorry, the changelog should be: if a system uses acpi_pm clocksource but
default idle method then the overhead of entry/exit measurement is quite
noticeable in profiles. The measurement is redundant anyway, as in HLT
sched_clock() is still supposed to work fine. (the worst i know of is a
slight skew on certain CPUs in HLT)

Ingo


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