Date: Wed, 24 Oct 2012 20:08:32 +0100 From: Attilio Rao <attilio@freebsd.org> To: Jim Harris <jim.harris@gmail.com> Cc: svn-src-head@freebsd.org, Adrian Chadd <adrian@freebsd.org>, src-committers@freebsd.org, svn-src-all@freebsd.org Subject: Re: svn commit: r242014 - head/sys/kern Message-ID: <CAJ-FndBOTHu=9j2DK9StzEQ5aq%2BmttZ8_T3TxjbJ7BvFhc03jg@mail.gmail.com> In-Reply-To: <CAJP=Hc9XmvfW3MrDjvK15OAx1fyfjPk%2BEhqHUOzoEpChu5imtg@mail.gmail.com> References: <201210241836.q9OIafqo073002@svn.freebsd.org> <CAJ-VmonpdJ445hXVaoHqFgS0v7QRwqHWodQrVHm2CN9T661www@mail.gmail.com> <CAJP=Hc9XmvfW3MrDjvK15OAx1fyfjPk%2BEhqHUOzoEpChu5imtg@mail.gmail.com>
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On Wed, Oct 24, 2012 at 7:56 PM, Jim Harris <jim.harris@gmail.com> wrote: > 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. While you may want to bring CACHE_LINE_SIZE to 64, code in sched_ule should still use CACHE_LINE_SIZE, as MI code cannot make assumption on cache line sizes for all the architectures. Your reasons for using 64 are valid, but a further next step to cleanup CACHE_LINE_SIZE and then use it properly in sched_ule are due IMHO. Attilio -- Peace can only be achieved by understanding - A. Einstein
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