* [PATCH] Move mostly read variables to __read_mostly section.
@ 2011-10-23 18:23 Eial Czerwacki
2011-10-24 4:47 ` Andi Kleen
0 siblings, 1 reply; 3+ messages in thread
From: Eial Czerwacki @ 2011-10-23 18:23 UTC (permalink / raw)
To: linux-kernel; +Cc: Shai Fultheim (Shai@ScaleMP.com)
Move mostly read variables to __read_mostly section.
Signed-off-by: Eial Czerwacki<eial@ScaleMP.com>
Signed-off-by: Shai Fultheim<Shai@ScaleMP.com>
---
--- a/fs/buffer.c 2010-05-12 14:59:32.000000000 -0700
+++ b/fs/buffer.c 2010-05-24 11:56:32.000000000 -0700
@@ -3233,7 +3233,7 @@ SYSCALL_DEFINE2(bdflush, int, func, long
/*
* Buffer-head allocation
*/
-static struct kmem_cache *bh_cachep;
+static struct kmem_cache __read_mostly *bh_cachep;
/*
* 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;
static struct timespec total_sleep_time;
/*
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] Move mostly read variables to __read_mostly section.
2011-10-23 18:23 [PATCH] Move mostly read variables to __read_mostly section Eial Czerwacki
@ 2011-10-24 4:47 ` Andi Kleen
2011-10-25 7:25 ` Eial Czerwacki
0 siblings, 1 reply; 3+ messages in thread
From: Andi Kleen @ 2011-10-24 4:47 UTC (permalink / raw)
To: Eial Czerwacki; +Cc: linux-kernel, Shai Fultheim (Shai@ScaleMP.com)
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
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] Move mostly read variables to __read_mostly section.
2011-10-24 4:47 ` Andi Kleen
@ 2011-10-25 7:25 ` Eial Czerwacki
0 siblings, 0 replies; 3+ messages in thread
From: Eial Czerwacki @ 2011-10-25 7:25 UTC (permalink / raw)
To: Andi Kleen; +Cc: linux-kernel, Shai Fultheim (Shai@ScaleMP.com)
On 10/24/2011 06:47 AM, Andi Kleen wrote:
> 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
Hello Andi,
Thanks for the input, we've removed the mentioned above section from the
patch and it will be handled in a different patch.
the new patch is as follows:
Signed-off-by: Eial Czerwacki<eial@ScaleMP.com>
Signed-off-by: Shai Fultheim<Shai@ScaleMP.com>
---
--- a/fs/buffer.c 2010-05-12 14:59:32.000000000 -0700
+++ b/fs/buffer.c 2010-05-24 11:56:32.000000000 -0700
@@ -3233,7 +3233,7 @@ SYSCALL_DEFINE2(bdflush, int, func, long
/*
* Buffer-head allocation
*/
-static struct kmem_cache *bh_cachep;
+static struct kmem_cache __read_mostly *bh_cachep;
/*
* Once the number of bh's in the machine exceeds this level, we start
^ permalink raw reply [flat|nested] 3+ messages in thread
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