Date: Wed, 24 Oct 2012 11:56:31 -0700 From: Jim Harris <jim.harris@gmail.com> To: Adrian Chadd <adrian@freebsd.org> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org Subject: Re: svn commit: r242014 - head/sys/kern Message-ID: <CAJP=Hc9XmvfW3MrDjvK15OAx1fyfjPk%2BEhqHUOzoEpChu5imtg@mail.gmail.com> In-Reply-To: <CAJ-VmonpdJ445hXVaoHqFgS0v7QRwqHWodQrVHm2CN9T661www@mail.gmail.com> References: <201210241836.q9OIafqo073002@svn.freebsd.org> <CAJ-VmonpdJ445hXVaoHqFgS0v7QRwqHWodQrVHm2CN9T661www@mail.gmail.com>
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On Wed, Oct 24, 2012 at 11:41 AM, Adrian Chadd <adrian@freebsd.org> wrote: > On 24 October 2012 11:36, Jim Harris <jimharris@freebsd.org> wrote: > >> Pad tdq_lock to avoid false sharing with tdq_load and tdq_cpu_idle. > > Ok, but.. > > >> struct mtx tdq_lock; /* run queue lock. */ >> + char pad[64 - sizeof(struct mtx)]; > > .. don't we have an existing compile time macro for the cache line > size, which can be used here? Yes, but I didn't use it for a couple of reasons: 1) struct tdq itself is currently using __aligned(64), so I wanted to keep it consistent. 2) CACHE_LINE_SIZE is currently defined as 128 on x86, due to NetBurst-based processors having 128-byte cache sectors a while back. I had planned to start a separate thread on arch@ about this today on whether this was still appropriate. > > > Adrian
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