Date: Wed, 31 Oct 2012 21:31:41 +0100 From: Andre Oppermann <andre@freebsd.org> To: Ian Lepore <freebsd@damnhippie.dyndns.org> Cc: Adrian Chadd <adrian@freebsd.org>, src-committers@freebsd.org, svn-src-all@freebsd.org, Attilio Rao <attilio@freebsd.org>, svn-src-head@freebsd.org, Peter Jeremy <peter@rulingia.com> Subject: Re: svn commit: r242402 - in head/sys: kern vm Message-ID: <50918AAD.2090906@freebsd.org> In-Reply-To: <1351712425.1120.109.camel@revolution.hippie.lan> References: <201210311807.q9VI7IcX000993@svn.freebsd.org> <CAJ-FndDRkBS57e9mzZoJWX5ugJ0KBGxhMSO50KB8Wm8MFudjCA@mail.gmail.com> <1351707964.1120.97.camel@revolution.hippie.lan> <CAJ-FndC7QwpNAjzQTumqTY6Sj_RszXPwc0pbHv2-pRGMqbw0ww@mail.gmail.com> <CAJ-VmokqEFX4wQYh-ojo3kcWUPj5L-V_k0Nj-u3sQByVypkDFw@mail.gmail.com> <CAJ-FndCL7bpkbfaaR%2BaYQAxEBDmgip0QbrE5JhwnbTicSraz9g@mail.gmail.com> <20121031193020.GJ3309@server.rulingia.com> <1351712425.1120.109.camel@revolution.hippie.lan>
next in thread | previous in thread | raw e-mail | index | archive | help
On 31.10.2012 20:40, Ian Lepore wrote: > On Thu, 2012-11-01 at 06:30 +1100, Peter Jeremy wrote: >> On 2012-Oct-31 18:57:37 +0000, Attilio Rao <attilio@FreeBSD.org> wrote: >>> On 10/31/12, Adrian Chadd <adrian@freebsd.org> wrote: >>>> Right, but you didn't make it configurable for us embedded peeps who >>>> still care about memory usage. >>> >>> How is this possible without breaking the module/kernel ABI? >> >> Memory usage may override ABI compatibility in an embedded environment. >> >>> All that assuming you can actually prove a real performance loss even >>> in the new cases. >> >> The issue with padding on embedded systems is memory utilisation rather >> than performance. >> > > There are potential performance hits too, in that embedded systems tend > to have tiny caches (16K L1 with no L2, that sort of thing), so > purposely padding things so that large parts of a cache line aren't used > for anything wastes a scarce resource. You can define CACHE_LINE_SIZE to 0 on those platforms. Or to make it even more granular there could be a CACHE_LINE_SIZE_LOCKS that is used for lock padding. -- Andre > That said, I think a point Attilio was trying to make is that we won't > see a large hit because this doesn't affect a large number of mutex > instances. I'm willing to accept his expert advice on that, not in > small part because I'm not sure how I'd go about disputing it. :) > > I'm really busy with $work right now, but things should calm down in a > couple weeks, and I'd be willing to do some measurements on arm systems > then, if I can get some help on how to generate useful data. > > -- Ian > > > >
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?50918AAD.2090906>