Date: Sun, 29 Mar 2015 14:15:43 -0700 From: Adrian Chadd <adrian@freebsd.org> To: Gleb Smirnoff <glebius@freebsd.org> Cc: Hans Petter Selasky <hps@selasky.org>, "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>, Fabien Thomas <fabient@freebsd.org> Subject: Re: svn commit: r280759 - head/sys/netinet Message-ID: <CAJ-VmomQzEXV4KtokK7jBgqCHEwExvYxhHJBar1uY2=yB1BjAg@mail.gmail.com> In-Reply-To: <20150329210757.GA64665@FreeBSD.org> References: <201503271326.t2RDQxd3056112@svn.freebsd.org> <20150328083443.GV64665@FreeBSD.org> <20150328191629.GY64665@FreeBSD.org> <5517B433.5010508@selasky.org> <CAJ-VmonU15_nEGVQNwR52deDf1TbPUz0oAMr%2B3zwNqU_9%2Bo1fw@mail.gmail.com> <20150329210757.GA64665@FreeBSD.org>
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> To illustrate the probability of 1 instruction race, I would suggest to > look at PCPU_ADD() implementation for all arches except amd64/i386 and > find out that it is prone to this race. Hitting the race in PCPU_ADD() > will usually lead to mangling vm_meter statistics. Did we ever observe > this in practice? No. I dunno. Has anyone actually looked at that? :) On a busy system you may find those small race windows exist enough to be annoying. Case in point - the recent callout code race. The race between "read" "modify" "write" was tiny, but enough to break things. -adrian
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