From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id AAAF2C282C0 for ; Thu, 24 Jan 2019 01:06:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 76E9D21872 for ; Thu, 24 Jan 2019 01:06:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727093AbfAXBGt convert rfc822-to-8bit (ORCPT ); Wed, 23 Jan 2019 20:06:49 -0500 Received: from ozlabs.org ([203.11.71.1]:42993 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726313AbfAXBGs (ORCPT ); Wed, 23 Jan 2019 20:06:48 -0500 Received: from authenticated.ozlabs.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (P-256) server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPSA id 43lPBG45Pmz9sCX; Thu, 24 Jan 2019 12:06:46 +1100 (AEDT) From: Michael Ellerman To: Christophe Leroy , Benjamin Herrenschmidt , Paul Mackerras , Nicholas Piggin Cc: Mike Rapoport , linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v13 00/10] powerpc: Switch to CONFIG_THREAD_INFO_IN_TASK In-Reply-To: <2e700e1c-5bd9-652e-b535-68a89dd703a1@c-s.fr> References: <2e700e1c-5bd9-652e-b535-68a89dd703a1@c-s.fr> Date: Thu, 24 Jan 2019 12:06:45 +1100 Message-ID: <87y37ax3ru.fsf@concordia.ellerman.id.au> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Christophe Leroy writes: > Le 12/01/2019 à 10:55, Christophe Leroy a écrit : >> The purpose of this serie is to activate CONFIG_THREAD_INFO_IN_TASK which >> moves the thread_info into task_struct. >> >> Moving thread_info into task_struct has the following advantages: >> - It protects thread_info from corruption in the case of stack >> overflows. >> - Its address is harder to determine if stack addresses are >> leaked, making a number of attacks more difficult. > > I ran null_syscall and context_switch benchmark selftests and the result > is surprising. There is slight degradation in context_switch and a > significant one on null_syscall: > > Without the serie: > > ~# chrt -f 98 ./context_switch --no-altivec --no-vector --no-fp > 55542 > 55562 > 55564 > 55562 > 55568 > ... > > ~# ./null_syscall > 2546.71 ns 336.17 cycles > > > With the serie: > > ~# chrt -f 98 ./context_switch --no-altivec --no-vector --no-fp > 55138 > 55142 > 55152 > 55144 > 55142 > > ~# ./null_syscall > 3479.54 ns 459.30 cycles > > So 0,8% less context switches per second and 37% more time for one syscall ? > > Any idea ? What platform is that on? On 64-bit we have to turn one mtmsrd into two and that's obviously a slow down. But I don't see that you've done anything similar in 32-bit code. I assume it's patch 8 that causes the slow down? cheers