Messages in this thread | | | Subject | Re: [RFC] time: xtime_lock is held too long | From | Eric Dumazet <> | Date | Fri, 06 May 2011 03:41:43 +0200 |
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Le jeudi 05 mai 2011 à 23:01 +0200, Andi Kleen a écrit : > > > Another idea would be to prime cache lines to be dirtied in cpu cache > > > before taking locks, and better pack variables to reduce number of cache > > > lines. > > > > Most variables are packed already in struct timekeeper, which should > > be pretty cache hot anyway, so I don't know whether we gain much. > > There's actually some potential here. I got a moderate speedup in a > database benchmark with this patch recently. The biggest win > was in the timer interrupt. > > All those variables are on separate cache lines. > > (needs some cleanups, just for illustration) > > -Andi > > From: Andi Kleen <ak@linux.intel.com> > Subject: [PATCH] do prefetches for timer state in timer interrupt > > diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c > index 76b96d7..2704267 100644 > --- a/arch/x86/kernel/apic/apic.c > +++ b/arch/x86/kernel/apic/apic.c > @@ -856,6 +856,17 @@ void __irq_entry smp_apic_timer_interrupt(struct pt_regs *regs) > { > struct pt_regs *old_regs = set_irq_regs(regs); > > + extern struct timespec xtime; > + extern struct timespec wall_to_monotonic; > + > + > + /* Prefetch here to make the ktime_get later faster. > + * XXX move them all on the same cache line. > + */ > + prefetch(&xtime_lock); > + prefetch(&xtime); > + prefetch(&wall_to_monotonic); > + > /* > * NOTE! We'd better ACK the irq immediately, > * because timer handling can be slow. > diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c > index d27c756..0002e9e 100644 > --- a/kernel/time/timekeeping.c > +++ b/kernel/time/timekeeping.c > @@ -157,8 +157,8 @@ __cacheline_aligned_in_smp DEFINE_SEQLOCK(xtime_lock); > * - wall_to_monotonic is no longer the boot time, getboottime must be > * used instead. > */ > -static struct timespec xtime __attribute__ ((aligned (16))); > -static struct timespec wall_to_monotonic __attribute__ ((aligned (16))); > +struct timespec xtime __attribute__ ((aligned (16))); > +struct timespec wall_to_monotonic __attribute__ ((aligned (16))); > static struct timespec total_sleep_time; > > /* >
Did you tried prefetchw() by any chance ?
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