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Wed, 15 Mar 2023 12:36:28 -0400 X-MC-Unique: 0_two9ifOYW8-fQttFHzIw-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.rdu2.redhat.com [10.11.54.8]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id DCA38858297; Wed, 15 Mar 2023 16:36:26 +0000 (UTC) Received: from warthog.procyon.org.uk (unknown [10.33.36.18]) by smtp.corp.redhat.com (Postfix) with ESMTP id C161AC164E7; Wed, 15 Mar 2023 16:36:24 +0000 (UTC) From: David Howells To: Jens Axboe , Al Viro , Christoph Hellwig Cc: David Howells , Matthew Wilcox , Jan Kara , Jeff Layton , David Hildenbrand , Jason Gunthorpe , Logan Gunthorpe , Hillf Danton , Christian Brauner , Linus Torvalds , linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Christoph Hellwig , John Hubbard Subject: [PATCH v19 11/15] block: Fix bio_flagged() so that gcc can better optimise it Date: Wed, 15 Mar 2023 16:35:45 +0000 Message-Id: <20230315163549.295454-12-dhowells@redhat.com> In-Reply-To: <20230315163549.295454-1-dhowells@redhat.com> References: <20230315163549.295454-1-dhowells@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 9C5CB180016 X-Rspam-User: X-Stat-Signature: hdfp69jc6y48j6juamyawrp5f9ac58s7 X-HE-Tag: 1678898194-283591 X-HE-Meta: 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 D8z5qH6y sdoqrgLOz3a9E7bd+Z2kXjiLbZ5yBG7koJNzD0WB06ouP+AAHds74jput4fMkUheXPVuvWyCO+qUJZXrJOspQg2GW9GZC80Gb/QGQjl2SfTSocNU760871a5i7PrmMAp3j5a8fclvCfIVyURQOz/RkFjs0NdmNtPqr4r1zPmqcd6A/wb36VEK0g+SX7Ou98UOmkRLnnWaR+AUu5EFBUGeu3jj2jq+N3icN0Rn7bEF2AvEt3SKdtVmkNvjq259thKiJfC44iX3/azDwEFy5yqr2N1gLx0cp8R8r3Am6ATqjPHO6T9dvkgJL5TiYGTf3uOL3E35K8u+umzNL6Ez2U+I0jopSCsJdgcHTi20LhfZ6Q5mz2Y6hvnKooBu0pZBlQZiAAVc9RDwK5dOGcBOHyipa5rMU4rausbSN3VOBbrbLJ9dY7li9OS47WAuubMDMquvRqUVW4/63/GLAQ1sGiXW+ilJtnyQ3p+sv0bAXRGUfQtMMXs= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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. Signed-off-by: David Howells Reviewed-by: Christoph Hellwig Reviewed-by: John Hubbard 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 d766be7152e1..d9d6df62ea57 100644 --- a/include/linux/bio.h +++ b/include/linux/bio.h @@ -229,7 +229,7 @@ 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)