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Subject[tip:x86/mm] x86: Avoid tlbstate lock if not enough cpus
Commit-ID:  7064d865af804b9b841e7b9a3e9b653e40c3e5ca
Gitweb: http://git.kernel.org/tip/7064d865af804b9b841e7b9a3e9b653e40c3e5ca
Author: Shaohua Li <shaohua.li@intel.com>
AuthorDate: Mon, 17 Jan 2011 10:52:10 +0800
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Mon, 14 Feb 2011 13:03:08 +0100

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>
---
arch/x86/mm/tlb.c | 11 ++++-------
1 files changed, 4 insertions(+), 7 deletions(-)

diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
index 6acc724..55272d7 100644
--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -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,

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