Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753907Ab0KCGon (ORCPT ); Wed, 3 Nov 2010 02:44:43 -0400 Received: from mga02.intel.com ([134.134.136.20]:1441 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753624Ab0KCGoa (ORCPT ); Wed, 3 Nov 2010 02:44:30 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.58,287,1286175600"; d="scan'208";a="673766292" Subject: [RFC 4/4]x86: avoid tlbstate lock if no enough cpus From: Shaohua Li To: lkml Cc: Ingo Molnar , Andi Kleen , "hpa@zytor.com" Content-Type: text/plain; charset="UTF-8" Date: Wed, 03 Nov 2010 14:44:28 +0800 Message-ID: <1288766668.23014.117.camel@sli10-conroe> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1767 Lines: 54 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 --- 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, -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/