Date: Mon, 05 Oct 2009 09:17:36 -0500 From: Alan Cox <alc@cs.rice.edu> To: John Baldwin <jhb@FreeBSD.org> Cc: Alan Cox <alc@FreeBSD.org>, svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org Subject: Re: svn commit: r197750 - head/sys/vm Message-ID: <4ACA0000.2080005@cs.rice.edu> In-Reply-To: <4AC9F4F4.4030008@FreeBSD.org> References: <200910041853.n94IrAf7082338@svn.freebsd.org> <4AC9F4F4.4030008@FreeBSD.org>
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John Baldwin wrote: > Alan Cox wrote: >> Author: alc >> Date: Sun Oct 4 18:53:10 2009 >> New Revision: 197750 >> URL: http://svn.freebsd.org/changeset/base/197750 >> >> Log: >> Align and pad the page queue and free page queue locks so that the >> linker >> can't possibly place them together within the same cache line. >> MFC after: 3 weeks >> >> Modified: >> head/sys/vm/vm_page.c >> head/sys/vm/vm_page.h >> >> Modified: head/sys/vm/vm_page.c >> ============================================================================== >> >> --- head/sys/vm/vm_page.c Sun Oct 4 17:22:51 2009 (r197749) >> +++ head/sys/vm/vm_page.c Sun Oct 4 18:53:10 2009 (r197750) >> @@ -135,8 +135,8 @@ __FBSDID("$FreeBSD$"); >> */ >> >> struct vpgqueues vm_page_queues[PQ_COUNT]; >> -struct mtx vm_page_queue_mtx; >> -struct mtx vm_page_queue_free_mtx; >> +struct vpglocks vm_page_queue_lock; >> +struct vpglocks vm_page_queue_free_lock; > > I think you can do this by just: > > struct mtx vm_page_queue_mtx __aligned(CACHE_LINE_SIZE); > > without the need for a wrapper structure. > Unfortunately, no. When I compile the following example: int a; int b __attribute__((aligned(16))); int x; int y; int z; int main(void) { return (0); } I get the following: 080495b4 A __bss_start 080495b4 A _edata 080495c0 b completed.4860 080495c4 B environ 080495d0 B b 080495d4 B x 080495d8 B z 080495dc B y 080495e0 B a 080495e4 A _end Thus, "b" is aligned as specified, but not padded to 16 bytes. Alan
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