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[2620:137:e000::1:20]) by mx.google.com with ESMTP id i13-20020a63e90d000000b00480a937f894si43422719pgh.766.2023.01.20.10.13.24; Fri, 20 Jan 2023 10:13:36 -0800 (PST) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; dkim=pass header.i=@redhat.com header.s=mimecast20190719 header.b=DeSAX4KN; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230247AbjATR6r (ORCPT + 99 others); Fri, 20 Jan 2023 12:58:47 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46892 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229711AbjATR61 (ORCPT ); Fri, 20 Jan 2023 12:58:27 -0500 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 65164521F6 for ; Fri, 20 Jan 2023 09:56:22 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1674237381; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=BIdz+Kfhb3Mbi+adj+F0X2Vrzxptw0enhnglhrMvwYk=; b=DeSAX4KNZ3ajIPpPDXj7N2pCuWauK7KKHjUE0ejEkqD4ogL+dxCEm7qbUJLe05TFFK2LfI FyLtDOKOwUnkwUZ4+brt83kdTFeajpSRDQy23L6UMxpt4DJdMaOAHpydFAJoQLT1Oa2JGn rZFOPLAdavfBl/FuAPCyV2UrDuavEN8= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-552-eICs1qe3OOy62k6d_alEGg-1; Fri, 20 Jan 2023 12:56:18 -0500 X-MC-Unique: eICs1qe3OOy62k6d_alEGg-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 52365811E9C; Fri, 20 Jan 2023 17:56:17 +0000 (UTC) Received: from warthog.procyon.org.uk.com (unknown [10.33.36.23]) by smtp.corp.redhat.com (Postfix) with ESMTP id E11401759E; Fri, 20 Jan 2023 17:56:15 +0000 (UTC) From: David Howells To: Al Viro , Christoph Hellwig Cc: David Howells , Matthew Wilcox , Jens Axboe , Jan Kara , Jeff Layton , Logan Gunthorpe , linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, Christoph Hellwig Subject: [PATCH v7 7/8] block: Fix bio_flagged() so that gcc can better optimise it Date: Fri, 20 Jan 2023 17:55:55 +0000 Message-Id: <20230120175556.3556978-8-dhowells@redhat.com> In-Reply-To: <20230120175556.3556978-1-dhowells@redhat.com> References: <20230120175556.3556978-1-dhowells@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.5 X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE, RCVD_IN_MSPIKE_H2,SPF_HELO_NONE,SPF_NONE autolearn=unavailable autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1755566222024420561?= X-GMAIL-MSGID: =?utf-8?q?1755566222024420561?= Fix bio_flagged() so that multiple instances of it, such as: if (bio_flagged(bio, BIO_PAGE_REFFED) || bio_flagged(bio, BIO_PAGE_PINNED)) can be combined by the gcc optimiser into a single test in assembly (arguably, this is a compiler optimisation issue[1]). The missed optimisation stems from bio_flagged() comparing the result of the bitwise-AND to zero. This results in an out-of-line bio_release_page() being compiled to something like: <+0>: mov 0x14(%rdi),%eax <+3>: test $0x1,%al <+5>: jne 0xffffffff816dac53 <+7>: test $0x2,%al <+9>: je 0xffffffff816dac5c <+11>: movzbl %sil,%esi <+15>: jmp 0xffffffff816daba1 <__bio_release_pages> <+20>: jmp 0xffffffff81d0b800 <__x86_return_thunk> However, the test is superfluous as the return type is bool. Removing it results in: <+0>: testb $0x3,0x14(%rdi) <+4>: je 0xffffffff816e4af4 <+6>: movzbl %sil,%esi <+10>: jmp 0xffffffff816dab7c <__bio_release_pages> <+15>: jmp 0xffffffff81d0b7c0 <__x86_return_thunk> instead. Also, the MOVZBL instruction looks unnecessary[2] - I think it's just 're-booling' the mark_dirty parameter. Fixes: b7c44ed9d2fc ("block: manipulate bio->bi_flags through helpers") Signed-off-by: David Howells Reviewed-by: Christoph Hellwig cc: Jens Axboe cc: linux-block@vger.kernel.org Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108370 [1] Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108371 [2] Link: https://lore.kernel.org/r/167391056756.2311931.356007731815807265.stgit@warthog.procyon.org.uk/ # v6 --- include/linux/bio.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/linux/bio.h b/include/linux/bio.h index 1c6f051f6ff2..2e6109b0fca8 100644 --- a/include/linux/bio.h +++ b/include/linux/bio.h @@ -227,7 +227,7 @@ static inline void bio_cnt_set(struct bio *bio, unsigned int count) static inline bool bio_flagged(struct bio *bio, unsigned int bit) { - return (bio->bi_flags & (1U << bit)) != 0; + return bio->bi_flags & (1U << bit); } static inline void bio_set_flag(struct bio *bio, unsigned int bit)