From: Andi Kleen <andi@firstfloor.org>
To: Eial Czerwacki <eial@scalemp.com>
Cc: linux-kernel@vger.kernel.org,
"Shai Fultheim \(Shai\@ScaleMP.com\)" <Shai@scalemp.com>
Subject: Re: [PATCH] Move mostly read variables to __read_mostly section.
Date: Sun, 23 Oct 2011 21:47:45 -0700 [thread overview]
Message-ID: <m2sjmj572m.fsf@firstfloor.org> (raw)
In-Reply-To: <4EA45BB8.20505@scalemp.com> (Eial Czerwacki's message of "Sun, 23 Oct 2011 20:23:52 +0200")
Eial Czerwacki <eial@scalemp.com> writes:
> * Once the number of bh's in the machine exceeds this level, we start
> --- a/kernel/time/timekeeping.c 2010-05-12 14:59:32.000000000 -0700
> +++ b/kernel/time/timekeeping.c 2010-05-24 11:56:32.000000000 -0700
> @@ -154,7 +154,7 @@ __cacheline_aligned_in_smp DEFINE_SEQLOC
> * used instead.
> */
> static struct timespec xtime __attribute__ ((aligned (16)));
> -static struct timespec wall_to_monotonic __attribute__ ((aligned (16)));
> +static struct timespec wall_to_monotonic __attribute__ ((aligned
> (16))) __read_mostly;
That means that a common time fetch/update call will usually have to fetch two
cachelines now instead of one, because it needs xtime and
wall_to_monotonic. Usually those end up nearby.
On the other hand it's rare to fetch wall_to_monotonic without xtime.
So if anything all those variables should be grouped together in a
single cacheline, but definitely not split like you do.
The other changes in your patch are fine for me.
-Andi
--
ak@linux.intel.com -- Speaking for myself only
next prev parent reply other threads:[~2011-10-24 4:47 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-10-23 18:23 [PATCH] Move mostly read variables to __read_mostly section Eial Czerwacki
2011-10-24 4:47 ` Andi Kleen [this message]
2011-10-25 7:25 ` Eial Czerwacki
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