[PATCH 1/2] cgroup: rstat: use same convention to assign cgroup_base_stat

[PATCH 1/2] cgroup: rstat: use same convention to assign cgroup_base_stat

[Wei Yang]

In function cgroup_base_stat_flush(), we update cgroup_base_stat by
getting rstatc->bstat and adjust delta to related fields.

There are two convention to assign cgroup_base_stat in this function:

  * rstat2 = rstat1
  * rstat2.cputime = rstat1.cputime

The second convention may make audience think just field "cputime" is
updated, while cputime is the only field in cgroup_base_stat.

Let's use the same convention to eliminate this confusion.

Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
---
 kernel/cgroup/rstat.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/cgroup/rstat.c b/kernel/cgroup/rstat.c
index a00875375f7d..c626d5a526c4 100644
--- a/kernel/cgroup/rstat.c
+++ b/kernel/cgroup/rstat.c
@@ -324,7 +324,7 @@ static void cgroup_base_stat_flush(struct cgroup *cgrp, int cpu)
 	/* fetch the current per-cpu values */
 	do {
 		seq = __u64_stats_fetch_begin(&rstatc->bsync);
-		cur.cputime = rstatc->bstat.cputime;
+		cur = rstatc->bstat;
 	} while (__u64_stats_fetch_retry(&rstatc->bsync, seq));
 
 	/* propagate percpu delta to global */
-- 
2.33.1

[PATCH 2/2] cgroup: rstat: retrieve current bstat to delta directly

[Wei Yang]

Instead of retrieve current bstat to cur and copy it to delta, let's use
delta directly.

This saves one copy operation and has the same code convention as
propagating delta to parent.

Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
---
 kernel/cgroup/rstat.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/kernel/cgroup/rstat.c b/kernel/cgroup/rstat.c
index c626d5a526c4..f66944c53613 100644
--- a/kernel/cgroup/rstat.c
+++ b/kernel/cgroup/rstat.c
@@ -314,7 +314,7 @@ static void cgroup_base_stat_flush(struct cgroup *cgrp, int cpu)
 {
 	struct cgroup_rstat_cpu *rstatc = cgroup_rstat_cpu(cgrp, cpu);
 	struct cgroup *parent = cgroup_parent(cgrp);
-	struct cgroup_base_stat cur, delta;
+	struct cgroup_base_stat delta;
 	unsigned seq;
 
 	/* Root-level stats are sourced from system-wide CPU stats */
@@ -324,11 +324,10 @@ static void cgroup_base_stat_flush(struct cgroup *cgrp, int cpu)
 	/* fetch the current per-cpu values */
 	do {
 		seq = __u64_stats_fetch_begin(&rstatc->bsync);
-		cur = rstatc->bstat;
+		delta = rstatc->bstat;
 	} while (__u64_stats_fetch_retry(&rstatc->bsync, seq));
 
 	/* propagate percpu delta to global */
-	delta = cur;
 	cgroup_base_stat_sub(&delta, &rstatc->last_bstat);
 	cgroup_base_stat_add(&cgrp->bstat, &delta);
 	cgroup_base_stat_add(&rstatc->last_bstat, &delta);
-- 
2.33.1

Re: [PATCH 1/2] cgroup: rstat: use same convention to assign cgroup_base_stat

[Tejun Heo]

On Sat, Jan 08, 2022 at 12:38:16AM +0000, Wei Yang wrote:
> In function cgroup_base_stat_flush(), we update cgroup_base_stat by
> getting rstatc->bstat and adjust delta to related fields.
> 
> There are two convention to assign cgroup_base_stat in this function:
> 
>   * rstat2 = rstat1
>   * rstat2.cputime = rstat1.cputime
> 
> The second convention may make audience think just field "cputime" is
> updated, while cputime is the only field in cgroup_base_stat.
> 
> Let's use the same convention to eliminate this confusion.
> 
> Signed-off-by: Wei Yang <richard.weiyang@gmail.com>

Applied 1-2 to cgroup/for-5.18.

Thanks.

-- 
tejun