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authorFeng Tang <feng.tang@intel.com>2020-08-06 23:23:11 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2020-08-07 11:33:26 -0700
commit0a4954a850b0c4d0a5d18b1a55d6e5a653e362b5 (patch)
tree28dc147820ec43d7c15f4e8c51e024b8eebd02c0
parent4e2ee51e82510813969eff9feff8e570a8a28c73 (diff)
downloadlinux-0a4954a850b0c4d0a5d18b1a55d6e5a653e362b5.tar.bz2
percpu_counter: add percpu_counter_sync()
percpu_counter's accuracy is related to its batch size. For a percpu_counter with a big batch, its deviation could be big, so when the counter's batch is runtime changed to a smaller value for better accuracy, there could also be requirment to reduce the big deviation. So add a percpu-counter sync function to be run on each CPU. Reported-by: kernel test robot <rong.a.chen@intel.com> Signed-off-by: Feng Tang <feng.tang@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Cc: Dennis Zhou <dennis@kernel.org> Cc: Tejun Heo <tj@kernel.org> Cc: Christoph Lameter <cl@linux.com> Cc: Michal Hocko <mhocko@suse.com> Cc: Qian Cai <cai@lca.pw> Cc: Andi Kleen <andi.kleen@intel.com> Cc: Huang Ying <ying.huang@intel.com> Cc: Dave Hansen <dave.hansen@intel.com> Cc: Haiyang Zhang <haiyangz@microsoft.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Kees Cook <keescook@chromium.org> Cc: "K. Y. Srinivasan" <kys@microsoft.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Mel Gorman <mgorman@suse.de> Cc: Tim Chen <tim.c.chen@intel.com> Link: http://lkml.kernel.org/r/1594389708-60781-4-git-send-email-feng.tang@intel.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--include/linux/percpu_counter.h4
-rw-r--r--lib/percpu_counter.c19
2 files changed, 23 insertions, 0 deletions
diff --git a/include/linux/percpu_counter.h b/include/linux/percpu_counter.h
index 0a4f54dd4737..01861eebed79 100644
--- a/include/linux/percpu_counter.h
+++ b/include/linux/percpu_counter.h
@@ -44,6 +44,7 @@ void percpu_counter_add_batch(struct percpu_counter *fbc, s64 amount,
s32 batch);
s64 __percpu_counter_sum(struct percpu_counter *fbc);
int __percpu_counter_compare(struct percpu_counter *fbc, s64 rhs, s32 batch);
+void percpu_counter_sync(struct percpu_counter *fbc);
static inline int percpu_counter_compare(struct percpu_counter *fbc, s64 rhs)
{
@@ -172,6 +173,9 @@ static inline bool percpu_counter_initialized(struct percpu_counter *fbc)
return true;
}
+static inline void percpu_counter_sync(struct percpu_counter *fbc)
+{
+}
#endif /* CONFIG_SMP */
static inline void percpu_counter_inc(struct percpu_counter *fbc)
diff --git a/lib/percpu_counter.c b/lib/percpu_counter.c
index a66595ba5543..a2345de90e93 100644
--- a/lib/percpu_counter.c
+++ b/lib/percpu_counter.c
@@ -99,6 +99,25 @@ void percpu_counter_add_batch(struct percpu_counter *fbc, s64 amount, s32 batch)
EXPORT_SYMBOL(percpu_counter_add_batch);
/*
+ * For percpu_counter with a big batch, the devication of its count could
+ * be big, and there is requirement to reduce the deviation, like when the
+ * counter's batch could be runtime decreased to get a better accuracy,
+ * which can be achieved by running this sync function on each CPU.
+ */
+void percpu_counter_sync(struct percpu_counter *fbc)
+{
+ unsigned long flags;
+ s64 count;
+
+ raw_spin_lock_irqsave(&fbc->lock, flags);
+ count = __this_cpu_read(*fbc->counters);
+ fbc->count += count;
+ __this_cpu_sub(*fbc->counters, count);
+ raw_spin_unlock_irqrestore(&fbc->lock, flags);
+}
+EXPORT_SYMBOL(percpu_counter_sync);
+
+/*
* Add up all the per-cpu counts, return the result. This is a more accurate
* but much slower version of percpu_counter_read_positive()
*/