Date: Mon, 05 Dec 2005 23:31:34 +0100 From: Andre Oppermann <andre@freebsd.org> To: John Baldwin <jhb@freebsd.org> Cc: cvs-src@freebsd.org, src-committers@freebsd.org, cvs-all@freebsd.org Subject: Re: cvs commit: src/sys/kern subr_witness.c src/sys/sys _lock.h lock.h Message-ID: <4394BFC6.E66F23A1@freebsd.org> References: <200512052045.jB5KjOQv050836@repoman.freebsd.org> <200512051552.47724.jhb@freebsd.org>
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John Baldwin wrote: > > On Monday 05 December 2005 03:45 pm, John Baldwin wrote: > > jhb 2005-12-05 20:45:24 UTC > > > > FreeBSD src repository > > > > Modified files: > > sys/kern subr_witness.c > > sys/sys _lock.h lock.h > > Log: > > Tweak witness handling of lock object to shave 2 pointers off of each > > lock object (and thus off of each mutex and sx lock): > > > > ... > > > > With these changes, struct mtx shrinks from 36 to 28 bytes on 32-bit > > platforms and from 72 to 56 bytes on 64-bit platforms. Note that this > > commit will completely and utterly destroy the kernel ABI, so no MFC. > > > > Tested on: alpha, amd64, i386, sparc64 > > andre@ reported a 5% perf increase from this change on at least one network > benchmark. I tested only with WITNESS enabled and there it did in fact make a 5% difference on a HTTP connection performance test over the loopback interface. It is mostly limited by lock performance and I was measuring only 33 instructions on average between two lock operations (lock or unlock). -- Andre
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