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>
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 @@
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 @@
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,