Date: Sat, 18 Aug 2007 08:50:41 -0700 From: Alfred Perlstein <alfred@freebsd.org> To: Pawel Jakub Dawidek <pjd@FreeBSD.org> Cc: freebsd-arch@FreeBSD.org Subject: Re: Lockless uidinfo. Message-ID: <20070818155041.GY90381@elvis.mu.org> In-Reply-To: <20070818150028.GD6498@garage.freebsd.pl> References: <20070818120056.GA6498@garage.freebsd.pl> <20070818142337.GW90381@elvis.mu.org> <20070818150028.GD6498@garage.freebsd.pl>
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* Pawel Jakub Dawidek <pjd@FreeBSD.org> [070818 07:59] wrote: > On Sat, Aug 18, 2007 at 07:23:37AM -0700, Alfred Perlstein wrote: > > * Pawel Jakub Dawidek <pjd@FreeBSD.org> [070818 05:31] wrote: > > > Hi. > > > > > > The patch below remove per-uidinfo locks: > > > > > > http://people.freebsd.org/~pjd/patches/uidinfo_lockless.patch > > > > In uifree() is it ok to manually check the refcount for 0? > > > > I'm gussing the hashmtx is used as a barrier? > > Yes, to lookup uidinfo you need to hold uihashtbl_mtx mutex, so once you > hold it and ui_ref is 0, noone will be able to reference it, because it > has to wait to look it up. And the field doesn't need to be volatile to prevent cached/opportunitic reads? -- - Alfred Perlstein
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