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x86: Avoid tlbstate lock if not enough cpus

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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>
Acked-by: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Andi Kleen <andi@firstfloor.org>
LKML-Reference: <1295232730.1949.710.camel@sli10-conroe>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Shaohua Li 2011-01-17 10:52:10 +08:00 committed by Ingo Molnar
parent 70e4a36973
commit 7064d865af
1 changed files with 4 additions and 7 deletions
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11
arch/x86/mm/tlb.c
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@ -179,12 +179,8 @@ static void flush_tlb_others_ipi(const struct cpumask *cpumask,
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 struct cpumask *cpumask,
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,