Date: Fri, 27 May 2016 15:34:25 -0500 From: Eric van Gyzen <vangyzen@FreeBSD.org> To: Mateusz Guzik <mjguzik@gmail.com>, freebsd-current@freebsd.org Subject: Re: [PATCH] microoptimize locking primitives by avoiding unnecessary atomic ops Message-ID: <84b595b1-7fb4-efd9-dc2f-9faac90da1e0@FreeBSD.org> In-Reply-To: <20160527191700.GA23039@dft-labs.eu> References: <20160527191700.GA23039@dft-labs.eu>
next in thread | previous in thread | raw e-mail | index | archive | help
On 05/27/16 02:17 PM, Mateusz Guzik wrote: > Hello there, > > quite some time ago I posted a trivial patch to locking primitives. What > they do is the inline part tries an atomic op and if that fails the > actual function is called, which immediately tries the same op. > > The obvious optimisation checks for the availability of the lock first. > > There concerns about the way it was done previously by relying on > volatile behaving in a specific way. > > Later a simplified version was posted which should not have the concern, > but the thread died. > > I refer you to https://lists.freebsd.org/pipermail/freebsd-current/2015-November/058100.html > for simple benchmark results. > > I would like to get the patch in before 11 freeze. This makes sense to me, and the patch looks good. Please consider adding a comment to each location that explains why the extra condition is tested before the atomic op. Without such a comment, I am concerned that your changes will be garbage collected later, because the extra condition would seem superfluous to someone less familiar with the code. Eric
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?84b595b1-7fb4-efd9-dc2f-9faac90da1e0>