Commit 7064d865 authored Jan 17, 2011 by Shaohua Li Committed by Ingo Molnar Feb 14, 2011

x86: Avoid tlbstate lock if not enough cpus



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>

parent 70e4a369

arch/x86/mm/tlb.c

+4 −7

Original line number	Diff line number	Diff line
		@@ -179,11 +179,7 @@ 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.
		*/
		if (nr_cpu_ids > NUM_INVALIDATE_TLB_VECTORS)
		raw_spin_lock(&f->tlbstate_lock);

		f->flush_mm = mm;
		@@ -202,6 +198,7 @@ static void flush_tlb_others_ipi(const struct cpumask *cpumask,

		f->flush_mm = NULL;
		f->flush_va = 0;
		if (nr_cpu_ids > NUM_INVALIDATE_TLB_VECTORS)
		raw_spin_unlock(&f->tlbstate_lock);
		}