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=-15.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 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 C5D97C433EF for ; Sat, 11 Sep 2021 22:01:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 94D5C60F38 for ; Sat, 11 Sep 2021 22:01:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231295AbhIKWCb (ORCPT ); Sat, 11 Sep 2021 18:02:31 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49120 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229800AbhIKWCb (ORCPT ); Sat, 11 Sep 2021 18:02:31 -0400 Received: from mail-il1-x132.google.com (mail-il1-x132.google.com [IPv6:2607:f8b0:4864:20::132]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 28941C061574 for ; Sat, 11 Sep 2021 15:01:18 -0700 (PDT) Received: by mail-il1-x132.google.com with SMTP id b15so5503373ils.10 for ; Sat, 11 Sep 2021 15:01:18 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel-dk.20150623.gappssmtp.com; s=20150623; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=tQSkm6tCbl9Wf/cyiD5+MIIKsbApY2RlMKuMatkf1ZY=; b=jpaMkAttgkd0x1sc8sa//V9ndlQx7vYA2oKsOFoaijSGFp4H1lTzzqV0mBezfRXVpj 9WWYiVftNrcZtLLaISHuEpV32JsgKGtWtjYJpKO/kkzumy2ag9m5U8P4b6OGzwp2H63L 7tELljXb1jlIwrfGmMec+VfsvqcYbtl/N0VFTs9fUdZY9XAX9OhSyxXzEA8yyoYpXtX4 wZzjJoNfLZve+R71JiHSQdFDvAd1onJ6jOlk2eabHWAqzRyP8Sdms4sAUaH+8e9J4RL6 ugJPCLCXgRZjZGEBW1DT0wvYTxLVi2LGthHtTencbBaUo0uMGFllBaaEid2b8A6H7pJ0 WGjQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=tQSkm6tCbl9Wf/cyiD5+MIIKsbApY2RlMKuMatkf1ZY=; b=8GNTggc9nPBwDtxeFeaTs2aNCbNO2ATjbuvWgnjDeXK4gGYZf9zstYJx4JmTRt0bCW WwA6FSW5d+jiH3faE2WPhL7Y3e12qTfvpOFTEFw+qRSnaOqHpSpvt93l1iBzNV0XVFiV SDhvd6nKbD6nsxPKd4mf8lTgT4CLK0kVki2DGR2Sr+RFrnXqt4p0xPdwe894nRAEgPOB 6ekvt5tVEbKU8ARZzD3gncoc6rxLDxaHsmwqsQo8aLyDAE0JaTGJa4PLYT7xmCiaQc6B gD0a6XPaBuBCrThvDulhfEtQyRnZJ0pnQH+VwmRz5sJ2cUbfFgYLCdc7X5Hy7Hf6cTgi bggw== X-Gm-Message-State: AOAM533P3xvK/J9lxZjskNJjRBJt7bvTXObym4xv6nNCModQuhk3zljD VWj+EOkxjk1ptPRl21SVQzFTcQ== X-Google-Smtp-Source: ABdhPJxNrCFovEy9MlSgaJYElflh/c0wSpbpImYIkAhUq59DyHACAqk6gXcOEqQYqjaiv88ZGad6Zg== X-Received: by 2002:a92:ca84:: with SMTP id t4mr2571339ilo.41.1631397677327; Sat, 11 Sep 2021 15:01:17 -0700 (PDT) Received: from [192.168.1.116] ([66.219.217.159]) by smtp.gmail.com with ESMTPSA id h11sm1620128ilc.7.2021.09.11.15.01.16 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 11 Sep 2021 15:01:16 -0700 (PDT) Subject: Re: [PATCH] block: Optimize bio_init() To: Bart Van Assche Cc: linux-block@vger.kernel.org, Christoph Hellwig References: <20210911214734.4692-1-bvanassche@acm.org> From: Jens Axboe Message-ID: Date: Sat, 11 Sep 2021 16:01:16 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20210911214734.4692-1-bvanassche@acm.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 9/11/21 3:47 PM, Bart Van Assche wrote: > The following test: > > sudo taskset -c 0 t/io_uring -b512 -d128 -c32 -s32 -p1 -F1 -B1 /dev/nullb0 > > reports 1366 K IOPS on my test setup without this patch and 1380 K IOPS > with this patch applied. In other words, this patch realizes a 1% > performance improvement. I think this is because this patch makes the > compiler generate better code. See also commit da521626ac62 ("bio: > optimize initialization of a bio"). > > The assembler code generated by gcc without this patch is as follows: > > 0x0000000000000000 <+0>: call 0x5 > 0x0000000000000005 <+5>: xor %eax,%eax > 0x0000000000000007 <+7>: xor %ecx,%ecx > 0x0000000000000009 <+9>: movl $0x1,0x1c(%rdi) > 0x0000000000000010 <+16>: movq $0x0,(%rdi) > 0x0000000000000017 <+23>: movq $0x0,0x8(%rdi) > 0x000000000000001f <+31>: movq $0x0,0x10(%rdi) > 0x0000000000000027 <+39>: mov %ax,0x18(%rdi) > 0x000000000000002b <+43>: movb $0x0,0x1a(%rdi) > 0x000000000000002f <+47>: movq $0x0,0x20(%rdi) > 0x0000000000000037 <+55>: movq $0x0,0x28(%rdi) > 0x000000000000003f <+63>: movl $0x0,0x30(%rdi) > 0x0000000000000046 <+70>: movq $0x0,0x38(%rdi) > 0x000000000000004e <+78>: movq $0x0,0x40(%rdi) > 0x0000000000000056 <+86>: movq $0x0,0x48(%rdi) > 0x000000000000005e <+94>: movq $0x0,0x50(%rdi) > 0x0000000000000066 <+102>: movq $0x0,0x58(%rdi) > 0x000000000000006e <+110>: movq $0x0,0x60(%rdi) > 0x0000000000000076 <+118>: mov %cx,0x68(%rdi) > 0x000000000000007a <+122>: movl $0x1,0x6c(%rdi) > 0x0000000000000081 <+129>: mov %dx,0x6a(%rdi) > 0x0000000000000085 <+133>: mov %rsi,0x70(%rdi) > 0x0000000000000089 <+137>: movq $0x0,0x78(%rdi) > 0x0000000000000091 <+145>: ret > > With this patch bio_init() is compiled into the following assembly code: > > 0x0000000000000000 <+0>: call 0x5 > 0x0000000000000005 <+5>: mov %rdi,%r8 > 0x0000000000000008 <+8>: mov $0x10,%ecx > 0x000000000000000d <+13>: xor %eax,%eax > 0x000000000000000f <+15>: rep stos %rax,%es:(%rdi) > 0x0000000000000012 <+18>: movl $0x1,0x1c(%r8) > 0x000000000000001a <+26>: mov %dx,0x6a(%r8) > 0x000000000000001f <+31>: movl $0x1,0x6c(%r8) > 0x0000000000000027 <+39>: mov %rsi,0x70(%r8) > 0x000000000000002b <+43>: ret > > Cc: Christoph Hellwig > Signed-off-by: Bart Van Assche > --- > block/bio.c | 45 ++++++++------------------------------------- > 1 file changed, 8 insertions(+), 37 deletions(-) > > diff --git a/block/bio.c b/block/bio.c > index 5df3dd282e40..775cd4274523 100644 > --- a/block/bio.c > +++ b/block/bio.c > @@ -244,47 +244,18 @@ static void bio_free(struct bio *bio) > } > > /* > - * Users of this function have their own bio allocation. Subsequently, > - * they must remember to pair any call to bio_init() with bio_uninit() > - * when IO has completed, or when the bio is released. > + * Users of this function must pair any call to bio_init() with a call to > + * bio_uninit() after IO has completed or when the bio is released. > */ > void bio_init(struct bio *bio, struct bio_vec *table, > unsigned short max_vecs) > { > - bio->bi_next = NULL; > - bio->bi_bdev = NULL; > - bio->bi_opf = 0; > - bio->bi_flags = 0; > - bio->bi_ioprio = 0; > - bio->bi_write_hint = 0; > - bio->bi_status = 0; > - bio->bi_iter.bi_sector = 0; > - bio->bi_iter.bi_size = 0; > - bio->bi_iter.bi_idx = 0; > - bio->bi_iter.bi_bvec_done = 0; > - bio->bi_end_io = NULL; > - bio->bi_private = NULL; > -#ifdef CONFIG_BLK_CGROUP > - bio->bi_blkg = NULL; > - bio->bi_issue.value = 0; > -#ifdef CONFIG_BLK_CGROUP_IOCOST > - bio->bi_iocost_cost = 0; > -#endif > -#endif > -#ifdef CONFIG_BLK_INLINE_ENCRYPTION > - bio->bi_crypt_context = NULL; > -#endif > -#ifdef CONFIG_BLK_DEV_INTEGRITY > - bio->bi_integrity = NULL; > -#endif > - bio->bi_vcnt = 0; > - > - atomic_set(&bio->__bi_remaining, 1); > - atomic_set(&bio->__bi_cnt, 1); > - > - bio->bi_max_vecs = max_vecs; > - bio->bi_io_vec = table; > - bio->bi_pool = NULL; > + *bio = (struct bio) { > + .__bi_remaining = ATOMIC_INIT(1), > + .__bi_cnt = ATOMIC_INIT(1), > + .bi_max_vecs = max_vecs, > + .bi_io_vec = table, > + }; > } I'll give this a whirl too, another upside is that it's less prone to errors if struct bio is changed. -- Jens Axboe