Messages in this thread | | | Date | Fri, 3 Jul 2009 10:04:48 +0800 | Subject | Re: [RFC patch] Use IPI_shortcut for lapic timer broadcast | From | Luming Yu <> |
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On Fri, Jul 3, 2009 at 8:23 AM, Pallipadi, Venkatesh<venkatesh.pallipadi@intel.com> wrote: > On Tue, 2009-06-30 at 00:01 -0700, Luming Yu wrote: >> Thanks for review. How about the following patch? >> >> /**The patch is enclosed in text attachment** >> **Using web client to send the patch** >> **below is for review, please apply attached patch*/ >> >> >> Signed-off-by: Yu Luming <luming.yu@intel.com> >> >> apic.c | 5 ++++- >> apic_flat_64.c | 7 ++++++- >> 2 files changed, 10 insertions(+), 2 deletions(-) >> >> >> --- linux-2.6.30-rc6/arch/x86/kernel/apic/apic.c.0 2009-06-29 >> 23:45:05.000000000 -0600 >> +++ linux-2.6.30-rc6/arch/x86/kernel/apic/apic.c 2009-06-30 >> 00:37:56.000000000 -0600 >> @@ -419,7 +419,10 @@ >> static void lapic_timer_broadcast(const struct cpumask *mask) >> { >> #ifdef CONFIG_SMP >> - apic->send_IPI_mask(mask, LOCAL_TIMER_VECTOR); >> + if (unlikely(cpumask_weight(mask) == num_online_cpus() -1)) >> + apic->send_IPI_all(LOCAL_TIMER_VECTOR); >> + else >> + apic->send_IPI_mask(mask, LOCAL_TIMER_VECTOR); >> #endif >> } > > I dont think it is a good idea to pay the penalty for cpumask_weight and > num_online_cpus, for the more common tickless case to fix this problem > with less common no tickeless case.
In NO_HZ, the lapic_timer_broadcast is rare thing too...
> > We should be able to add an interface to get tick_nohz_enabled from > tick-sched.c and use that instead.
If we use send_IPI_all just for NO_HZ is disabled, we will leave a corner case here that lapic_timer_broadcast could be really really being actively used even NO_HZ enabled... if this will never happen, I would agree with you..
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