Messages in this thread Patch in this message | | | Subject | Re: [RFC 4/4]x86: avoid tlbstate lock if no enough cpus | From | Shaohua Li <> | Date | Thu, 04 Nov 2010 13:21:19 +0800 |
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On Wed, 2010-11-03 at 17:08 +0800, Eric Dumazet wrote: > Le mercredi 03 novembre 2010 à 16:41 +0800, Shaohua Li a écrit : > > > yes, this is ok. we might need avoid some cpu hotplug race too. I'll > > post a new patch later. > > > > > > Hmm, maybe only set the variable "must take the lock", never unset it. I followed your suggestions to use nr_cpu_ids, it should be good enough.
Thanks, Shaohua
This one isn't related to previous patch. If online cpus are below NUM_INVALIDATE_TLB_VECTORS, we don't need the lock. The comments in the code declares we don't need the check, but a hot lock still needs an atomic operation and expensive, so add the check here.
Uses nr_cpu_ids here as suggested by Eric Dumazet.
Signed-off-by: Shaohua Li <shaohua.li@intel.com> --- arch/x86/mm/tlb.c | 11 ++++------- 1 file changed, 4 insertions(+), 7 deletions(-)
Index: linux/arch/x86/mm/tlb.c =================================================================== --- linux.orig/arch/x86/mm/tlb.c 2010-11-04 10:59:09.000000000 +0800 +++ linux/arch/x86/mm/tlb.c 2010-11-04 13:17:51.000000000 +0800 @@ -179,12 +179,8 @@ static void flush_tlb_others_ipi(const s sender = this_cpu_read(tlb_vector_offset); f = &flush_state[sender]; - /* - * Could avoid this lock when - * num_online_cpus() <= NUM_INVALIDATE_TLB_VECTORS, but it is - * probably not worth checking this for a cache-hot lock. - */ - raw_spin_lock(&f->tlbstate_lock); + if (nr_cpu_ids > NUM_INVALIDATE_TLB_VECTORS) + raw_spin_lock(&f->tlbstate_lock); f->flush_mm = mm; f->flush_va = va; @@ -202,7 +198,8 @@ static void flush_tlb_others_ipi(const s f->flush_mm = NULL; f->flush_va = 0; - raw_spin_unlock(&f->tlbstate_lock); + if (nr_cpu_ids > NUM_INVALIDATE_TLB_VECTORS) + raw_spin_unlock(&f->tlbstate_lock); } void native_flush_tlb_others(const struct cpumask *cpumask,
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