The patch titled
kernel/timekeeping: move xtime_cache to be in the same cache line as the lock
has been added to the -mm tree. Its filename is
kernel-timekeeping-move-xtime_cache-to-be-in-the-same-cache-line-as-the-lock.patch
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Subject: kernel/timekeeping: move xtime_cache to be in the same cache line as the lock
From: Richard Kennedy <richard@xxxxxxxxxxxxxxx>
Move xtime_cache to be in the same cache line as the lock, allowing
current_kernel_time() to access only one cache line
When running fio write tests on a 2 core machine, on some of the runs
'perf record -e cache_misses' shows current_kernel_time near the top of
the list of cache_misses with 5.5%.
On the other runs it's down at 0.05% so I'm assuming that the difference
is just down to which core the test client get run on.
This patch moves the xtime_cache variable near to the lock so that it only
need to access one cache line. With this applied it drops the
current_kernel_time cache_misses in the slow case to 4.5%
Signed-off-by: Richard Kennedy <richard@xxxxxxxxxxxxxxx>
Cc: John Stultz <johnstul@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/time/timekeeping.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff -puN kernel/time/timekeeping.c~kernel-timekeeping-move-xtime_cache-to-be-in-the-same-cache-line-as-the-lock kernel/time/timekeeping.c
--- a/kernel/time/timekeeping.c~kernel-timekeeping-move-xtime_cache-to-be-in-the-same-cache-line-as-the-lock
+++ a/kernel/time/timekeeping.c
@@ -137,6 +137,7 @@ static inline s64 timekeeping_get_ns_raw
*/
__cacheline_aligned_in_smp DEFINE_SEQLOCK(xtime_lock);
+static struct timespec xtime_cache __attribute__ ((aligned (16)));
/*
* The current time
@@ -165,7 +166,6 @@ struct timespec raw_time;
/* flag for if timekeeping is suspended */
int __read_mostly timekeeping_suspended;
-static struct timespec xtime_cache __attribute__ ((aligned (16)));
void update_xtime_cache(u64 nsec)
{
xtime_cache = xtime;
_
Patches currently in -mm which might be from richard@xxxxxxxxxxxxxxx are
kernel-timekeeping-move-xtime_cache-to-be-in-the-same-cache-line-as-the-lock.patch
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