Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752487Ab3FGGt5 (ORCPT ); Fri, 7 Jun 2013 02:49:57 -0400 Received: from mail.ispras.ru ([83.149.199.45]:43065 "EHLO mail.ispras.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751023Ab3FGGt4 (ORCPT ); Fri, 7 Jun 2013 02:49:56 -0400 Message-ID: <51B1828E.6060301@ispras.ru> Date: Fri, 07 Jun 2013 10:49:50 +0400 From: Alexey Khoroshilov User-Agent: Mozilla/5.0 (X11; Linux i686; rv:17.0) Gecko/20130510 Thunderbird/17.0.6 MIME-Version: 1.0 To: Steven Whitehouse CC: cluster-devel@redhat.com, linux-kernel@vger.kernel.org, ldv-project@linuxtesting.org Subject: Re: [PATCH] GFS2: minor readability improvement in gfs2_mount() References: <1370467772-4587-1-git-send-email-khoroshilov@ispras.ru> <1370510682.2744.5.camel@menhir> In-Reply-To: <1370510682.2744.5.camel@menhir> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2335 Lines: 58 Hi Steve, On 06/06/2013 01:24 PM, Steven Whitehouse wrote: > Hi, > > On Thu, 2013-06-06 at 01:29 +0400, Alexey Khoroshilov wrote: >> The patch makes usage pattern of IS_ERR-PTR_ERR more typical. >> >> Signed-off-by: Alexey Khoroshilov >> --- >> fs/gfs2/ops_fstype.c | 5 +++-- >> 1 file changed, 3 insertions(+), 2 deletions(-) >> >> diff --git a/fs/gfs2/ops_fstype.c b/fs/gfs2/ops_fstype.c >> index 0262c19..0d30e8e 100644 >> --- a/fs/gfs2/ops_fstype.c >> +++ b/fs/gfs2/ops_fstype.c >> @@ -1313,9 +1313,10 @@ static struct dentry *gfs2_mount(struct file_system_type *fs_type, int flags, >> } >> s = sget(fs_type, test_gfs2_super, set_gfs2_super, flags, bdev); >> mutex_unlock(&bdev->bd_fsfreeze_mutex); >> - error = PTR_ERR(s); >> - if (IS_ERR(s)) >> + if (IS_ERR(s)) { >> + error = PTR_ERR(s); >> goto error_bdev; >> + } > I'm not sure what you are getting at here. Why add a jump into the fast > path? My experiments with gcc 4.7.3 on x86-64 do not show any difference in code generated with patch and without it. 227a: e8 00 00 00 00 callq 227f 227b: R_X86_64_PC32 sget-0x4 227f: 4c 89 f7 mov %r14,%rdi 2282: 49 89 c4 mov %rax,%r12 2285: e8 00 00 00 00 callq 228a 2286: R_X86_64_PC32 mutex_unlock-0x4 228a: 49 81 fc 00 f0 ff ff cmp $0xfffffffffffff000,%r12 2291: 0f 87 2a 01 00 00 ja 23c1 2297: 49 83 7c 24 60 00 cmpq $0x0,0x60(%r12) 229d: 74 0b je 22aa 229f: 44 89 ee mov %r13d,%esi 22a2: 48 89 df mov %rbx,%rdi 22a5: e8 00 00 00 00 callq 22aa 22a6: R_X86_64_PC32 blkdev_put-0x4 It looks like 'error = PTR_ERR(s);' assignment is just ignored because s and error share the same register %r12. So the only point of the patch is to improve readability. -- Best regards, Alexey -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/