From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751444Ab1LFFcu (ORCPT ); Tue, 6 Dec 2011 00:32:50 -0500 Received: from mx3.mail.elte.hu ([157.181.1.138]:39763 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751068Ab1LFFct (ORCPT ); Tue, 6 Dec 2011 00:32:49 -0500 X-Greylist: delayed 56061 seconds by postgrey-1.27 at vger.kernel.org; Tue, 06 Dec 2011 00:32:49 EST Date: Tue, 6 Dec 2011 06:31:00 +0100 From: Ingo Molnar To: Shaohua Li Cc: Linus Torvalds , "linux-kernel@vger.kernel.org" , "mingo@redhat.com" , "hpa@zytor.com" , "akpm@linux-foundation.org" , "tglx@linutronix.de" , "linux-tip-commits@vger.kernel.org" Subject: Re: [tip:x86/mm] x86/mm: Avoid superflous leave_mm() in the TLB flush path Message-ID: <20111206053100.GA30784@elte.hu> References: <1323132020.22361.364.camel@sli10-conroe> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1323132020.22361.364.camel@sli10-conroe> User-Agent: Mutt/1.5.21 (2010-09-15) X-ELTE-SpamScore: -2.0 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-2.0 required=5.9 tests=AWL,BAYES_00 autolearn=no SpamAssassin version=3.3.1 -2.0 BAYES_00 BODY: Bayes spam probability is 0 to 1% [score: 0.0000] 0.0 AWL AWL: From: address is in the auto white-list Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Shaohua Li wrote: > On Tue, 2011-12-06 at 07:26 +0800, Linus Torvalds wrote: > > On Mon, Dec 5, 2011 at 9:56 AM, tip-bot for Shaohua Li > > wrote: > > > > > > x86/mm: Avoid superflous leave_mm() in the TLB flush path > > > > > > If just one page VA tlb is required to be flushed and current > > > task is in lazy TLB state, doing leave_mm() is superfluous > > > because it flushes the whole TLB. This can reduce some TLB > > > miss. > > > > Are you sure this is a good idea? > > > > We may be *much* better off leaving the VM and avoiding future IPI's > > than trying to flush pages one by one over and over again. > > > > IPI's are expensive. > > > > I don't think you thought this through, and if you *did* think it > > through and actually have numbers that it's cheaper to stay with the > > MM, I think you need to show those numbers. > > good point, I didn't think of it. It's unlikely we just flush > one tlb page. please drop the patch. Dropped, thanks guys. Ingo