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=-13.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_IN_DEF_DKIM_WL autolearn=no 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 08CE1C433B4 for ; Wed, 14 Apr 2021 17:35:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BFCF061168 for ; Wed, 14 Apr 2021 17:35:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1350423AbhDNRft (ORCPT ); Wed, 14 Apr 2021 13:35:49 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46972 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230221AbhDNRfs (ORCPT ); Wed, 14 Apr 2021 13:35:48 -0400 Received: from mail-yb1-xb35.google.com (mail-yb1-xb35.google.com [IPv6:2607:f8b0:4864:20::b35]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B7AC0C061574 for ; Wed, 14 Apr 2021 10:35:26 -0700 (PDT) Received: by mail-yb1-xb35.google.com with SMTP id v72so2305715ybe.11 for ; Wed, 14 Apr 2021 10:35:26 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=p5oTNX1UW2iJQdYcROOOcZNjI/fXWbVj+c5HC1onlBc=; b=QpKoexFmzPklTyxAMaYaPU5L75FKBqSSi5CKQktpWyDTTpRNBuD+vCvJsbwlg46J63 iYQLO9RxSm/QmnE2DfirQnuvk9f7suzgNZN1ElOUy6J++ctSXRVjPYxuck1hFiT8ptLB hEemUpoFPSDF7dfglyI+7VrBYQOc097N2wl+YgRLq2eY4yPPLyZCbu6mxEOWPFzeRcRQ wpUNZ046CUmLT6fnCGBlpqEhXr5QMUjoOeNJdGb3uTDQmlKNQN3T0esh4z7NMru/K2Ix jhXAwF+85KxbOjhhjcgU2skzxi1O6THS3upeU3RbtunJKTw7njSmU9wMLJbXm1znbiSP qPOQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=p5oTNX1UW2iJQdYcROOOcZNjI/fXWbVj+c5HC1onlBc=; b=ZznKJ2/JK0TFJhUK5RT2FigQm3IsGA1aEVCDS7Y5WNHwk4WAVkgOwtKcs6OYzKBZ3A gy+F0KH2ZILMQqG7c+lCNI65s47xth46Kygn0TaD5hy37HXVRcxQhvUd6EnVPdwbSVdO 56O/94knRS2+CxwRXCDuXXyVGmcghmY/rhbv3Uxu+IIvATuLVjbsr1Co/2r4rf3dCMji lW8O3jN2lsuUNOoWXu5z7SNmNh9tnYT3wDvg1/4pTbGx76Y1fkb7NEQ1BtlAvgn4kbba 5WSRLlIaD3LDiNYES9cVCu05G09JgrNNweOjXV9P965HEmhbIXI+k9bK7ZsDO3JBGpyQ 6cjA== X-Gm-Message-State: AOAM531XK714o2xW/aQBA6yVj7b+8Dik0Nas0ERveU1aKJ+nUPSP6P9w MLT08JfTyZhtmp8DkyDox1DwhHdGJU+s5BeFhR+2Tw== X-Google-Smtp-Source: ABdhPJzr9gmGgEqSEs/nbYwpsh72AJN7ci9vJ+8aR/Zcp9/73jhjV+ceybUjuwM5GEvG+NpbPVgBCDSqKBfNvB2vk2E= X-Received: by 2002:a25:7650:: with SMTP id r77mr27382882ybc.446.1618421725696; Wed, 14 Apr 2021 10:35:25 -0700 (PDT) MIME-Version: 1.0 References: <20210413162240.3131033-1-eric.dumazet@gmail.com> <20210413162240.3131033-4-eric.dumazet@gmail.com> <567941475.72456.1618332885342.JavaMail.zimbra@efficios.com> <989543379.72506.1618334454075.JavaMail.zimbra@efficios.com> <1347243835.72576.1618336812739.JavaMail.zimbra@efficios.com> <2c6885b0241d4127b8cb7e38abbbe1e5@AcuMS.aculab.com> <1e5576a1a5b24cb0b1d53b9bb22d528e@AcuMS.aculab.com> In-Reply-To: From: Eric Dumazet Date: Wed, 14 Apr 2021 19:35:12 +0200 Message-ID: Subject: Re: [PATCH v2 3/3] rseq: optimise rseq_get_rseq_cs() and clear_rseq_cs() To: Arjun Roy Cc: David Laight , Mathieu Desnoyers , Eric Dumazet , Ingo Molnar , Peter Zijlstra , paulmck , Boqun Feng , linux-kernel Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Apr 14, 2021 at 7:15 PM Arjun Roy wrote: > > On Wed, Apr 14, 2021 at 9:10 AM Eric Dumazet wrote: > > > > On Wed, Apr 14, 2021 at 6:08 PM David Laight wrote: > > > > > > From: Eric Dumazet > > > > Sent: 14 April 2021 17:00 > > > ... > > > > > Repeated unsafe_get_user() calls are crying out for an optimisation. > > > > > You get something like: > > > > > failed = 0; > > > > > copy(); > > > > > if (failed) goto error; > > > > > copy(); > > > > > if (failed) goto error; > > > > > Where 'failed' is set by the fault handler. > > > > > > > > > > This could be optimised to: > > > > > failed = 0; > > > > > copy(); > > > > > copy(); > > > > > if (failed) goto error; > > > > > Even if it faults on every invalid address it probably > > > > > doesn't matter - no one cares about that path. > > > > > > > > > > > > On which arch are you looking at ? > > > > > > > > On x86_64 at least, code generation is just perfect. > > > > Not even a conditional jmp, it is all handled by exceptions (if any) > > > > > > > > stac > > > > copy(); > > > > copy(); > > > > clac > > > > > > > > > > > > > > > > efault_end: do error recovery. > > > > > > It will be x86_64. > > > I'm definitely seeing repeated tests of (IIRC) %rdx. > > > > > > It may well be because the compiler isn't very new. > > > Will be an Ubuntu build of 9.3.0. > > > Does that support 'asm goto with outputs' - which > > > may be the difference. > > > > > > > Yep, probably. I am using some recent clang version. > > > > On x86-64 I can confirm, for me it (4 x unsafe_get_user()) compiles > down to stac + lfence + 8 x mov + clac as straight line code. And > results in roughly a 5%-10% speedup over copy_from_user(). > But rseq_get_rseq_cs() would still need three different copies, with 3 stac+lfence+clac sequences. Maybe we need to enclose all __rseq_handle_notify_resume() operations in a single section. > -Arjun > > > > > David > > > > > > - > > > Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK > > > Registration No: 1397386 (Wales)