Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754164Ab0KDFVX (ORCPT ); Thu, 4 Nov 2010 01:21:23 -0400 Received: from mga11.intel.com ([192.55.52.93]:47329 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753470Ab0KDFVV (ORCPT ); Thu, 4 Nov 2010 01:21:21 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.58,293,1286175600"; d="scan'208";a="854020328" Subject: Re: [RFC 4/4]x86: avoid tlbstate lock if no enough cpus From: Shaohua Li To: Eric Dumazet Cc: lkml , Ingo Molnar , Andi Kleen , "hpa@zytor.com" In-Reply-To: <1288775282.2511.9.camel@edumazet-laptop> References: <1288766668.23014.117.camel@sli10-conroe> <1288767580.2467.636.camel@edumazet-laptop> <1288767995.23014.120.camel@sli10-conroe> <1288768330.2467.660.camel@edumazet-laptop> <1288768795.23014.123.camel@sli10-conroe> <1288769123.2467.681.camel@edumazet-laptop> <1288769486.2467.690.camel@edumazet-laptop> <1288773716.23014.124.camel@sli10-conroe> <1288775282.2511.9.camel@edumazet-laptop> Content-Type: text/plain; charset="UTF-8" Date: Thu, 04 Nov 2010 13:21:19 +0800 Message-ID: <1288848079.23014.131.camel@sli10-conroe> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2102 Lines: 63 On Wed, 2010-11-03 at 17:08 +0800, Eric Dumazet wrote: > Le mercredi 03 novembre 2010 à 16:41 +0800, Shaohua Li a écrit : > > > yes, this is ok. we might need avoid some cpu hotplug race too. I'll > > post a new patch later. > > > > > > Hmm, maybe only set the variable "must take the lock", never unset it. I followed your suggestions to use nr_cpu_ids, it should be good enough. Thanks, Shaohua 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 --- arch/x86/mm/tlb.c | 11 ++++------- 1 file changed, 4 insertions(+), 7 deletions(-) Index: linux/arch/x86/mm/tlb.c =================================================================== --- linux.orig/arch/x86/mm/tlb.c 2010-11-04 10:59:09.000000000 +0800 +++ linux/arch/x86/mm/tlb.c 2010-11-04 13:17:51.000000000 +0800 @@ -179,12 +179,8 @@ static void flush_tlb_others_ipi(const s 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 s 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, -- 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/