Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932751AbbLHFms (ORCPT ); Tue, 8 Dec 2015 00:42:48 -0500 Received: from mail-ob0-f172.google.com ([209.85.214.172]:33557 "EHLO mail-ob0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932626AbbLHFmr (ORCPT ); Tue, 8 Dec 2015 00:42:47 -0500 MIME-Version: 1.0 In-Reply-To: <20151208044254.GA3058@gmail.com> References: <20151208044254.GA3058@gmail.com> From: Andy Lutomirski Date: Mon, 7 Dec 2015 21:42:27 -0800 Message-ID: Subject: Re: [PATCH 00/12] x86: Rewrite 64-bit syscall code To: Ingo Molnar Cc: Andy Lutomirski , X86 ML , "linux-kernel@vger.kernel.org" , Brian Gerst , Borislav Petkov , =?UTF-8?B?RnLDqWTDqXJpYyBXZWlzYmVja2Vy?= , Denys Vlasenko , Linus Torvalds 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: 2200 Lines: 51 On Mon, Dec 7, 2015 at 8:42 PM, Ingo Molnar wrote: > > * Andy Lutomirski wrote: > >> On Mon, Dec 7, 2015 at 1:51 PM, Andy Lutomirski wrote: >> >> > This is kind of like the 32-bit and compat code, except that I preserved the >> > fast path this time. I was unable to measure any significant performance >> > change on my laptop in the fast path. >> > >> > What do you all think? >> >> For completeness, if I zap the fast path entirely (see attached), I lose 20 >> cycles (148 cycles vs 128 cycles) on Skylake. Switching between movq and pushq >> for stack setup makes no difference whatsoever, interestingly. I haven't tried >> to figure out exactly where those 20 cycles go. > > So I asked for this before, and I'll do so again: could you please stick the cycle > granular system call performance test into a 'perf bench' variant so that: > > 1) More people can run it all on various pieces of hardware and help out quantify > the patches. > > 2) We can keep an eye on not regressing base system call performance in the > future, with a good in-tree testcase. > Is it okay if it's not particularly shiny or modular? The tool I'm using is here: https://git.kernel.org/cgit/linux/kernel/git/luto/misc-tests.git/tree/tight_loop/perf_self_monitor.c and I can certainly stick it into 'perf bench' pretty easily. Can I leave making it into a proper library to some future contributor? It's actually decently fancy. It allocates a perf self-monitoring instance that counts cycles, and then it takes a bunch of samples and discards any that flagged a context switch. It does some very rudimentary statistics on the rest. It's utterly devoid of a fancy UI, though. It works very well on native, and it works better than I had expected under KVM. (KVM traps RDPMC because neither Intel nor AMD has seen fit to provide any sensible way to virtualize RDPMC without exiting.) --Andy -- 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/