Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756008AbdGKPBK (ORCPT ); Tue, 11 Jul 2017 11:01:10 -0400 Received: from mail.kernel.org ([198.145.29.99]:41184 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755413AbdGKPBJ (ORCPT ); Tue, 11 Jul 2017 11:01:09 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A496522C98 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=luto@kernel.org MIME-Version: 1.0 In-Reply-To: <20170711113233.GA19177@codeblueprint.co.uk> References: <20170630124422.GA12077@codeblueprint.co.uk> <20170711113233.GA19177@codeblueprint.co.uk> From: Andy Lutomirski Date: Tue, 11 Jul 2017 08:00:47 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v4 00/10] PCID and improved laziness To: Matt Fleming Cc: Andy Lutomirski , X86 ML , "linux-kernel@vger.kernel.org" , Borislav Petkov , Linus Torvalds , Andrew Morton , Mel Gorman , "linux-mm@kvack.org" , Nadav Amit , Rik van Riel , Dave Hansen , Arjan van de Ven , Peter Zijlstra Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1694 Lines: 43 On Tue, Jul 11, 2017 at 4:32 AM, Matt Fleming wrote: > On Fri, 30 Jun, at 01:44:22PM, Matt Fleming wrote: >> On Thu, 29 Jun, at 08:53:12AM, Andy Lutomirski wrote: >> > *** Ingo, even if this misses 4.13, please apply the first patch before >> > *** the merge window. >> > >> > There are three performance benefits here: >> > >> > 1. TLB flushing is slow. (I.e. the flush itself takes a while.) >> > This avoids many of them when switching tasks by using PCID. In >> > a stupid little benchmark I did, it saves about 100ns on my laptop >> > per context switch. I'll try to improve that benchmark. >> > >> > 2. Mms that have been used recently on a given CPU might get to keep >> > their TLB entries alive across process switches with this patch >> > set. TLB fills are pretty fast on modern CPUs, but they're even >> > faster when they don't happen. >> > >> > 3. Lazy TLB is way better. We used to do two stupid things when we >> > ran kernel threads: we'd send IPIs to flush user contexts on their >> > CPUs and then we'd write to CR3 for no particular reason as an excuse >> > to stop further IPIs. With this patch, we do neither. >> >> Heads up, I'm gonna queue this for a run on SUSE's performance test >> grid. > > FWIW, I didn't see any change in performance with this series on a > PCID-capable machine. On the plus side, I didn't see any weird-looking > bugs either. > > Are your benchmarks available anywhere? https://git.kernel.org/pub/scm/linux/kernel/git/luto/misc-tests.git/ I did: $ ./context_switch_latency_64 0 process same and $ ./madvise_bounce_64 10k [IIRC -- it might have been a different loop count] --Andy