[PATCH 2/4] block/blk-iolatency: account per-cpu latency stats over possible CPUs

[Tao Cui]

From: Tao Cui <cuitao@xxxxxxxxxx>

iolatency_check_latencies() and iolatency_ssd_stat() iterate a blkg's
per-cpu latency stats with for_each_online_cpu().  When a CPU that has
accumulated io.latency samples goes offline, its bucket is skipped: the
check loop (which also resets) neither sums nor clears it, and the show
path under-reports.  On re-online the stranded samples are flushed into
a later check window, which can trigger a spurious throttle/scale
adjustment.

Fixes: d70675121546 ("block: introduce blk-iolatency io controller")
Fixes: 1fa2840e56f9 ("blk-iolatency: use a percentile approache for ssd's")
Signed-off-by: Tao Cui <cuitao@xxxxxxxxxx>
---
 block/blk-iolatency.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/block/blk-iolatency.c b/block/blk-iolatency.c
index 1cc33aa0b669..d6c401d6174c 100644
--- a/block/blk-iolatency.c
+++ b/block/blk-iolatency.c
@@ -523,7 +523,7 @@ static void iolatency_check_latencies(struct iolatency_grp *iolat, u64 now)
 
 	latency_stat_init(iolat, &stat);
 	preempt_disable();
-	for_each_online_cpu(cpu) {
+	for_each_possible_cpu(cpu) {
 		struct latency_stat *s;
 		s = per_cpu_ptr(iolat->stats, cpu);
 		latency_stat_sum(iolat, &stat, s);
@@ -924,7 +924,7 @@ static void iolatency_ssd_stat(struct iolatency_grp *iolat, struct seq_file *s)
 
 	latency_stat_init(iolat, &stat);
 	preempt_disable();
-	for_each_online_cpu(cpu) {
+	for_each_possible_cpu(cpu) {
 		struct latency_stat *s;
 		s = per_cpu_ptr(iolat->stats, cpu);
 		latency_stat_sum(iolat, &stat, s);
-- 
2.43.0