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=-5.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 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 C4757C433E0 for ; Mon, 8 Feb 2021 17:21:09 +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 D1B9C64EC4 for ; Mon, 8 Feb 2021 17:21:08 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D1B9C64EC4 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=csgroup.eu Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from bilbo.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 4DZCVB2889zDrbt for ; Tue, 9 Feb 2021 04:21:06 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=csgroup.eu (client-ip=93.17.236.30; helo=pegase1.c-s.fr; envelope-from=christophe.leroy@csgroup.eu; receiver=) Received: from pegase1.c-s.fr (pegase1.c-s.fr [93.17.236.30]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4DZCRz3WYLzDr6D for ; Tue, 9 Feb 2021 04:19:00 +1100 (AEDT) Received: from localhost (mailhub1-int [192.168.12.234]) by localhost (Postfix) with ESMTP id 4DZCRb5fJPzB09ZX; Mon, 8 Feb 2021 18:18:51 +0100 (CET) X-Virus-Scanned: Debian amavisd-new at c-s.fr Received: from pegase1.c-s.fr ([192.168.12.234]) by localhost (pegase1.c-s.fr [192.168.12.234]) (amavisd-new, port 10024) with ESMTP id XSVo4u6bn2Po; Mon, 8 Feb 2021 18:18:51 +0100 (CET) Received: from messagerie.si.c-s.fr (messagerie.si.c-s.fr [192.168.25.192]) by pegase1.c-s.fr (Postfix) with ESMTP id 4DZCRb4l28zB09ZV; Mon, 8 Feb 2021 18:18:51 +0100 (CET) Received: from localhost (localhost [127.0.0.1]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 1920E8B7BF; Mon, 8 Feb 2021 18:18:55 +0100 (CET) X-Virus-Scanned: amavisd-new at c-s.fr Received: from messagerie.si.c-s.fr ([127.0.0.1]) by localhost (messagerie.si.c-s.fr [127.0.0.1]) (amavisd-new, port 10023) with ESMTP id ZKnNnc_Cdu40; Mon, 8 Feb 2021 18:18:55 +0100 (CET) Received: from [192.168.4.90] (unknown [192.168.4.90]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 8592F8B7B2; Mon, 8 Feb 2021 18:18:51 +0100 (CET) Subject: Re: [PATCH 2/8] powerpc/signal: Add unsafe_copy_{vsx, fpr}_from_user() To: "Christopher M. Riedl" , linuxppc-dev@lists.ozlabs.org References: From: Christophe Leroy Message-ID: Date: Mon, 8 Feb 2021 18:18:42 +0100 User-Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: fr Content-Transfer-Encoding: 8bit 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: , Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Le 08/02/2021 à 18:14, Christopher M. Riedl a écrit : > On Sun Feb 7, 2021 at 4:12 AM CST, Christophe Leroy wrote: >> >> >> Le 06/02/2021 à 18:39, Christopher M. Riedl a écrit : >>> On Sat Feb 6, 2021 at 10:32 AM CST, Christophe Leroy wrote: >>>> >>>> >>>> Le 20/10/2020 à 04:01, Christopher M. Riedl a écrit : >>>>> On Fri Oct 16, 2020 at 10:48 AM CDT, Christophe Leroy wrote: >>>>>> >>>>>> >>>>>> Le 15/10/2020 à 17:01, Christopher M. Riedl a écrit : >>>>>>> Reuse the "safe" implementation from signal.c except for calling >>>>>>> unsafe_copy_from_user() to copy into a local buffer. Unlike the >>>>>>> unsafe_copy_{vsx,fpr}_to_user() functions the "copy from" functions >>>>>>> cannot use unsafe_get_user() directly to bypass the local buffer since >>>>>>> doing so significantly reduces signal handling performance. >>>>>> >>>>>> Why can't the functions use unsafe_get_user(), why does it significantly >>>>>> reduces signal handling >>>>>> performance ? How much significant ? I would expect that not going >>>>>> through an intermediate memory >>>>>> area would be more efficient >>>>>> >>>>> >>>>> Here is a comparison, 'unsafe-signal64-regs' avoids the intermediate buffer: >>>>> >>>>> | | hash | radix | >>>>> | -------------------- | ------ | ------ | >>>>> | linuxppc/next | 289014 | 158408 | >>>>> | unsafe-signal64 | 298506 | 253053 | >>>>> | unsafe-signal64-regs | 254898 | 220831 | >>>>> >>>>> I have not figured out the 'why' yet. As you mentioned in your series, >>>>> technically calling __copy_tofrom_user() is overkill for these >>>>> operations. The only obvious difference between unsafe_put_user() and >>>>> unsafe_get_user() is that we don't have asm-goto for the 'get' variant. >>>>> Instead we wrap with unsafe_op_wrap() which inserts a conditional and >>>>> then goto to the label. >>>>> >>>>> Implemenations: >>>>> >>>>> #define unsafe_copy_fpr_from_user(task, from, label) do { \ >>>>> struct task_struct *__t = task; \ >>>>> u64 __user *buf = (u64 __user *)from; \ >>>>> int i; \ >>>>> \ >>>>> for (i = 0; i < ELF_NFPREG - 1; i++) \ >>>>> unsafe_get_user(__t->thread.TS_FPR(i), &buf[i], label); \ >>>>> unsafe_get_user(__t->thread.fp_state.fpscr, &buf[i], label); \ >>>>> } while (0) >>>>> >>>>> #define unsafe_copy_vsx_from_user(task, from, label) do { \ >>>>> struct task_struct *__t = task; \ >>>>> u64 __user *buf = (u64 __user *)from; \ >>>>> int i; \ >>>>> \ >>>>> for (i = 0; i < ELF_NVSRHALFREG ; i++) \ >>>>> unsafe_get_user(__t->thread.fp_state.fpr[i][TS_VSRLOWOFFSET], \ >>>>> &buf[i], label); \ >>>>> } while (0) >>>>> >>>> >>>> Do you have CONFIG_PROVE_LOCKING or CONFIG_DEBUG_ATOMIC_SLEEP enabled in >>>> your config ? >>> >>> I don't have these set in my config (ppc64le_defconfig). I think I >>> figured this out - the reason for the lower signal throughput is the >>> barrier_nospec() in __get_user_nocheck(). When looping we incur that >>> cost on every iteration. Commenting it out results in signal performance >>> of ~316K w/ hash on the unsafe-signal64-regs branch. Obviously the >>> barrier is there for a reason but it is quite costly. >> >> Interesting. >> >> Can you try with the patch I just sent out >> https://patchwork.ozlabs.org/project/linuxppc-dev/patch/c72f014730823b413528e90ab6c4d3bcb79f8497.1612692067.git.christophe.leroy@csgroup.eu/ > > Yeah that patch solves the problem. Using unsafe_get_user() in a loop is > actually faster on radix than using the intermediary buffer step. A > summary of results below (unsafe-signal64-v6 uses unsafe_get_user() and > avoids the local buffer): > > | | hash | radix | > | -------------------------------- | ------ | ------ | > | unsafe-signal64-v5 | 194533 | 230089 | > | unsafe-signal64-v6 | 176739 | 202840 | > | unsafe-signal64-v5+barrier patch | 203037 | 234936 | > | unsafe-signal64-v6+barrier patch | 205484 | 241030 | > > I am still expecting some comments/feedback on my v5 before sending out > v6. Should I include your patch in my series as well? > My patch is now flagged "under review" in patchwork so I suppose Michael picked it already. Christophe