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 B5D61C433F5 for ; Sat, 11 Sep 2021 22:16:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8E2D760F6C for ; Sat, 11 Sep 2021 22:16:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231415AbhIKWRx (ORCPT ); Sat, 11 Sep 2021 18:17:53 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52414 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229800AbhIKWRw (ORCPT ); Sat, 11 Sep 2021 18:17:52 -0400 Received: from mail-il1-x12c.google.com (mail-il1-x12c.google.com [IPv6:2607:f8b0:4864:20::12c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CCEF7C061574 for ; Sat, 11 Sep 2021 15:16:39 -0700 (PDT) Received: by mail-il1-x12c.google.com with SMTP id v16so1197191ilg.3 for ; Sat, 11 Sep 2021 15:16:39 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel-dk.20150623.gappssmtp.com; s=20150623; h=subject:from:to:cc:references:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=MEXTb3QcEM/ypIHuqN9qiQ/A1vfplVmsPUaky2RuJB8=; b=QIa2p+AHyVHLgiAlBIlCqtOGzsRzkwF9VKv5a8N2ciXr+C63nj1BYSrO6HYsoXeFM/ q68D+RoXLHnHl+YkHPhgZKso0MjZtnwqaKzqNfY2xqZu6bpu/TUYBqPrJ2dabdP7GhWk 1iTI3P2ao2ApOn0+rmVTgGBG66RcSSjJg8PjBsK0ys8jEVQgaDWnSG5iLc4NsYbJIqMr JlFdgTBB+ks96uuuJ22Kuep9HYMm94lxU+OVJo6EgFAkwneCr5h57CuyQmgteEKxTvm2 6MZu23nXna6K2NALHHka8P/GgiQxF1m/dXA/L0/QD6Wpo9d+7M10wh8u6dZlfg4O85Zv 9gQA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:subject:from:to:cc:references:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=MEXTb3QcEM/ypIHuqN9qiQ/A1vfplVmsPUaky2RuJB8=; b=nH3ImTG8PaWvJJjgG/XvpI9f7yrZ0VbdDPxiGAUmOrjKcXXvNM6Na17cghD3RCIVem LmTbbcoue2ATuEDZFyFzyLFCAdzyl+tJ9gJfT265bqETlQ+g43PtZCqQEmnwYDFSUZUK UXs37vakWrCm2aAWSurf8Yr9o1UaSoyG9dYanODYS7vPKgcETicgQGXLp5sGM3VEphUE Qbk7GqpLJQKNvxiPKIOnbOcMbhTzgPDCeY4Z0xnr6hNQDZrMsdec3D3x2jVUs2OMzexc wG7pWmAGTMp17HmMCT5lz3waAawpQDOR89dr1ik1zVM8soD5dVVOvdPdriDpS4WdLDI1 XasQ== X-Gm-Message-State: AOAM530EOeisoj5eM6FE+PVUD05D+2H94f6s2Or8q+hJ8Xk48oNbhEhI /SAnnZr9EE8x1CdpXgFk+NO/Wg== X-Google-Smtp-Source: ABdhPJzkt6shVWeRRMNxFW6sKgAUrxVgwITuXUH9drxeKFbqr30RnFjF41y54HBsgcUmrv14I72B6A== X-Received: by 2002:a92:c5c9:: with SMTP id s9mr2940206ilt.56.1631398599091; Sat, 11 Sep 2021 15:16:39 -0700 (PDT) Received: from [192.168.1.116] ([66.219.217.159]) by smtp.gmail.com with ESMTPSA id t14sm1604731ilu.67.2021.09.11.15.16.38 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 11 Sep 2021 15:16:38 -0700 (PDT) Subject: Re: [PATCH] block: Optimize bio_init() From: Jens Axboe To: Bart Van Assche Cc: linux-block@vger.kernel.org, Christoph Hellwig References: <20210911214734.4692-1-bvanassche@acm.org> Message-ID: Date: Sat, 11 Sep 2021 16:16:38 -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: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 9/11/21 4:09 PM, Jens Axboe wrote: > On 9/11/21 4:01 PM, Jens Axboe wrote: >> 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. > > Seems slower for me, by about 1-1.5%, which is consumed by > bio_alloc_kiocb() which is the only bio_init() caller in my test. Using > gcc 11.1 here, and my code generation seems to match your case too > (series of mov vs rep stos with the patch). > > Probably a CPU thing. I'm running on an AMD 3970X for these tests. Looking at profile: 43.34 │ rep stos %rax,%es:(%rdi) I do wonder if rep stos is just not very well suited for small regions, either in general or particularly on AMD. What do your profiles look like for before and after? -- Jens Axboe