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[49.179.78.197]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-20af17ee05dsm673315ad.123.2024.09.23.15.53.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 23 Sep 2024 15:53:06 -0700 (PDT) Received: from dave by dread.disaster.area with local (Exim 4.96) (envelope-from ) id 1ssrvT-009ArR-24; Tue, 24 Sep 2024 08:53:03 +1000 Date: Tue, 24 Sep 2024 08:53:03 +1000 From: Dave Chinner To: Uros Bizjak Cc: linux-xfs@vger.kernel.org, linux-kernel@vger.kernel.org, Christoph Hellwig , Chandan Babu R , "Darrick J. Wong" Subject: Re: [PATCH v3] xfs: Use try_cmpxchg() in xlog_cil_insert_pcp_aggregate() Message-ID: References: <20240923122311.914319-1-ubizjak@gmail.com> Precedence: bulk X-Mailing-List: linux-xfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240923122311.914319-1-ubizjak@gmail.com> On Mon, Sep 23, 2024 at 02:22:17PM +0200, Uros Bizjak wrote: > Use !try_cmpxchg instead of cmpxchg (*ptr, old, new) != old in > xlog_cil_insert_pcp_aggregate(). x86 CMPXCHG instruction returns > success in ZF flag, so this change saves a compare after cmpxchg. > > Also, try_cmpxchg implicitly assigns old *ptr value to "old" when > cmpxchg fails. There is no need to re-read the value in the loop. > > Note that the value from *ptr should be read using READ_ONCE to > prevent the compiler from merging, refetching or reordering the read. > > No functional change intended. > > Signed-off-by: Uros Bizjak > Reviewed-by: Christoph Hellwig > Cc: Chandan Babu R > Cc: "Darrick J. Wong" Looks fine. Reviewed-by: Dave Chinner -- Dave Chinner david@fromorbit.com