Messages in this thread Patch in this message | | | Subject | [RFC 4/4]x86: avoid tlbstate lock if no enough cpus | From | Shaohua Li <> | Date | Wed, 03 Nov 2010 14:44:28 +0800 |
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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.
Signed-off-by: Shaohua Li <shaohua.li@intel.com> --- arch/x86/mm/tlb.c | 14 +++++++------- 1 file changed, 7 insertions(+), 7 deletions(-)
Index: linux/arch/x86/mm/tlb.c =================================================================== --- linux.orig/arch/x86/mm/tlb.c 2010-11-02 10:31:51.000000000 +0800 +++ linux/arch/x86/mm/tlb.c 2010-11-02 14:53:27.000000000 +0800 @@ -174,17 +174,16 @@ static void flush_tlb_others_ipi(const s { unsigned int sender; union smp_flush_state *f; + bool do_lock = false; /* Caller has disabled preemption */ 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 (num_online_cpus() > NUM_INVALIDATE_TLB_VECTORS) { + do_lock = true; + raw_spin_lock(&f->tlbstate_lock); + } f->flush_mm = mm; f->flush_va = va; @@ -202,7 +201,8 @@ static void flush_tlb_others_ipi(const s f->flush_mm = NULL; f->flush_va = 0; - raw_spin_unlock(&f->tlbstate_lock); + if (do_lock) + raw_spin_unlock(&f->tlbstate_lock); } void native_flush_tlb_others(const struct cpumask *cpumask,
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