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 C5693C282C0 for ; Thu, 24 Jan 2019 01:08:19 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 4D0CF21872 for ; Thu, 24 Jan 2019 01:08:19 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4D0CF21872 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=ellerman.id.au Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 43lPD068MKzDqJS for ; Thu, 24 Jan 2019 12:08:16 +1100 (AEDT) Received: from ozlabs.org (bilbo.ozlabs.org [203.11.71.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 43lPBG6WG3zDqD3 for ; Thu, 24 Jan 2019 12:06:46 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=ellerman.id.au 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 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: quoted-printable X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, Mike Rapoport Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Christophe Leroy writes: > Le 12/01/2019 =C3=A0 10:55, Christophe Leroy a =C3=A9crit=C2=A0: >> The purpose of this serie is to activate CONFIG_THREAD_INFO_IN_TASK which >> moves the thread_info into task_struct. >>=20 >> 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= =20 > is surprising. There is slight degradation in context_switch and a=20 > 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 syscal= l ? > > 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