Date: Tue, 9 Apr 2013 23:57:51 +0400 From: Gleb Smirnoff <glebius@FreeBSD.org> To: John Baldwin <jhb@freebsd.org> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org Subject: Re: svn commit: r249265 - in head/sys: amd64/include arm/include i386/include ia64/include mips/include powerpc/include sparc64/include sys Message-ID: <20130409195751.GY76816@FreeBSD.org> In-Reply-To: <201304091520.25575.jhb@freebsd.org> References: <201304081919.r38JJAvB088644@svn.freebsd.org> <201304081541.27408.jhb@freebsd.org> <20130408194436.GI76816@FreeBSD.org> <201304091520.25575.jhb@freebsd.org>
next in thread | previous in thread | raw e-mail | index | archive | help
On Tue, Apr 09, 2013 at 03:20:25PM -0400, John Baldwin wrote:
J> > J> > Log:
J> > J> > Merge from projects/counters:
J> > J> >
J> > J> > Pad struct pcpu so that its size is denominator of PAGE_SIZE. This
J> > J> > is done to reduce memory waste in UMA_PCPU_ZONE zones.
J> > J> >
J> > J> > Sponsored by: Nginx, Inc.
J> > J> >
J> > J> > Modified: head/sys/sys/pcpu.h
J> > J> >
J> > J> ==============================================================================
J> > J> > --- head/sys/sys/pcpu.h Mon Apr 8 19:10:45 2013 (r249264)
J> > J> > +++ head/sys/sys/pcpu.h Mon Apr 8 19:19:10 2013 (r249265)
J> > J> > @@ -180,6 +180,14 @@ struct pcpu {
J> > J> > PCPU_MD_FIELDS;
J> > J> > } __aligned(CACHE_LINE_SIZE);
J> > J>
J> > J> Why not change this to be PAGE_SIZE rather than putting explicit padding in
J> > J> all the pcpu fields? That would seem to be more maintainable.
J> >
J> > Because it can be smaller than PAGE_SIZE. Two times smaller, four times smaller.
J>
J> Ugh, I didn't parse the "denominator" part correctly. I had read it as
J> "multiple". OTOH, it seems quite cheap even on a 32-bit platform to lose
J> 3k per core (assuming 4k page size and 1k pcpu).
There could be several UMA_ZONE_PCPU zones.
--
Totus tuus, Glebius.
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20130409195751.GY76816>