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Tue, 07 Feb 2017 15:40:54 -0800 (PST) Received: from [10.10.1.58] ([185.97.61.26]) by smtp.gmail.com with ESMTPSA id a13sm190495wma.13.2017.02.07.15.40.53 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 07 Feb 2017 15:40:53 -0800 (PST) Subject: Re: svn commit: r313260 - head/sys/kern To: Ed Maste <emaste@freebsd.org> References: <201702050140.v151eRXX090326@repo.freebsd.org> <42c790bb-df12-2a50-6181-24bac5c72d34@multiplay.co.uk> <20170205030006.GB4375@dft-labs.eu> <20170205151746.GA6841@FreeBSD.org> <20170207145750.GD4772@dft-labs.eu> <8e0f5a4c-16ec-842d-f4f7-32c830f43553@multiplay.co.uk> <CAPyFy2CcS4GxS-7VgWM49teOT0ZR8s0TVC+vVbnDZg_caHO2VA@mail.gmail.com> Cc: "svn-src-head@freebsd.org" <svn-src-head@freebsd.org>, "svn-src-all@freebsd.org" <svn-src-all@freebsd.org>, "src-committers@freebsd.org" <src-committers@freebsd.org>, Mateusz Guzik <mjg@freebsd.org> From: Steven Hartland <steven.hartland@multiplay.co.uk> Message-ID: <1a7c31e9-561c-9391-47f1-f25e5381b03f@multiplay.co.uk> Date: Tue, 7 Feb 2017 23:40:53 +0000 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.7.0 MIME-Version: 1.0 In-Reply-To: <CAPyFy2CcS4GxS-7VgWM49teOT0ZR8s0TVC+vVbnDZg_caHO2VA@mail.gmail.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit X-Content-Filtered-By: Mailman/MimeDel 2.1.23 X-BeenThere: svn-src-all@freebsd.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: "SVN commit messages for the entire src tree \(except for " user" and " projects" \)" <svn-src-all.freebsd.org> List-Unsubscribe: <https://lists.freebsd.org/mailman/options/svn-src-all>, <mailto:svn-src-all-request@freebsd.org?subject=unsubscribe> List-Archive: <http://lists.freebsd.org/pipermail/svn-src-all/> List-Post: <mailto:svn-src-all@freebsd.org> List-Help: <mailto:svn-src-all-request@freebsd.org?subject=help> List-Subscribe: <https://lists.freebsd.org/mailman/listinfo/svn-src-all>, <mailto:svn-src-all-request@freebsd.org?subject=subscribe> X-List-Received-Date: Tue, 07 Feb 2017 23:40:56 -0000 On 07/02/2017 20:34, Ed Maste wrote: > On 7 February 2017 at 10:30, Steven Hartland > <steven.hartland@multiplay.co.uk> wrote: >> All I'm suggesting is, while one could guess this may be a performance or >> possibly a compatibility thing, the reason is not obvious, so a small piece >> of detail on why the change was done should always be included. >> >> For this one something like the following would be nice: >> >> Switch fget_unlocked to atomic_fcmpset >> >> Improve performance under contention by switching fget_unlocked to >> use atomic_fcmpset. > I agree, and one of the key reasons to do this is so that there's this > tiny bit of context if someone later runs "git blame" or "svn > annotate" and discovers this change for the line containing > atomic_fcmpset. Comments containing "eliminate memory leak" or "remove > unused variable" have a self-evident reason, but I don't believe > that's true for "switch to atomic_fcmpset." > > Repeating the "switch fget_unlocked to..." in the proposed commit > message above feels redundant to me though, and I would suggest: > > | Switch fget_unlocked to atomic_fcmpset > | > | Improves performance under contention. > > or just: > > | Use atmoic_fcmpset to improve performance under contention All those work for me as they clearly state why the change was made, so I hope this is something we can try to improve moving forward :)