Received: by 2002:ad5:474a:0:0:0:0:0 with SMTP id i10csp1418685imu; Wed, 23 Jan 2019 17:08:23 -0800 (PST) X-Google-Smtp-Source: ALg8bN6Ux1IEwDGv+s9e4Ao/EDBLRWauIa2sCxCxz0Yart4Ri6nBCUWYFMp0FzufVxQ+UnrxADOL X-Received: by 2002:a63:dc0c:: with SMTP id s12mr4123825pgg.398.1548292103556; Wed, 23 Jan 2019 17:08:23 -0800 (PST) ARC-Seal: i=1; a=rsa-sha256; t=1548292103; cv=none; d=google.com; s=arc-20160816; b=bSwlqZZ7MFAvxQlwT0CLlyDzYyfpaZLM55/FicwxLyN3z8b+p6+5SKnM/SLJon5aGl 6/V+bUNL68Z5441iKTACYwoLgXYgSOAPeMoxLdPyQkNqKfaZJvUZP7eIZ/5Y9qaFYdDC zN0ooL7tuHON1Rz7eKx245mK0whh46MOv1u+R/Rvp9P8ZJsL0+mkyWsXzQWE2Jms6V47 o5w0i/pj8/wcMQBGBhEkwP6O3K44WjUiO7Qc0rs1Ir7J96T9fEJUX5LtECE/PyXP9YbZ ds8/hRFC2iBv06gPcP/YqSvpnSHak4soabA58bqiTLT8cy6UhPRdjiAWdRd883iNI+Hs PTlQ== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:sender:content-transfer-encoding:mime-version :message-id:date:references:in-reply-to:subject:cc:to:from; bh=MPMMarPwSxQdGs1Uyjme9Y6bUcz4Wi6nq4gVFpdgVYI=; b=ZGMXU6nxRpPSl3dMlH4zsNAmbKLvK7vlIDQnzgB8BGr3Hq3edQKWNWu5ayMgV4LhPt PEifvGtOSK4MGV6MvIU4dVN/f4BsGu58NaJcTcYfhwjLjPH1gUaBPpKXrSyj36rp2btl KNp+M/372X80yMmd/ircG+PnZD7zzNWwObhC21WKh+lQHWsgGat1dLqBUCrvHec759kr /wBcK3uVdnCfX9ibNzcGkDEte4bJTWq2xgJrqglrnAtjVCxicNLTXSJ7aZaiS/kHuU06 rQ49w/x0peEfnjd+5ykjFc3Wbqidm7LKlalX9VKH+HefoUnRbYgTSNZPjt3PrrIV4Trp h02A== ARC-Authentication-Results: i=1; mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Return-Path: Received: from vger.kernel.org (vger.kernel.org. [209.132.180.67]) by mx.google.com with ESMTP id f7si17550745pga.87.2019.01.23.17.08.02; Wed, 23 Jan 2019 17:08:23 -0800 (PST) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727077AbfAXBGs convert rfc822-to-8bit (ORCPT + 99 others); Wed, 23 Jan 2019 20:06:48 -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