Re: [PATCH] perf: update perf_cgroup time for ancestor cgroup(s)
> On Mar 12, 2018, at 5:38 AM, Peter Zijlstra wrote:
>
> On Sun, Mar 11, 2018 at 10:32:44PM -0700, Song Liu wrote:
>> When a perf_event is attached to parent cgroup, it should count events
>> for all children cgroups:
>>
>> parent_group < perf_event
>> \
>>- child_group < process(es)
>>
>> However, in our tests, we found this perf_event cannot report reliable
>> results. This is because perf_event->cgrp and cpuctx->cgrp are not
>> identical, thus perf_event->cgrp are not updated properly.
>
> It might help now and in for our older selves, if you could provide a
> simple reproducer for this.
I will add a repro to v2.
>
>> Signed-off-by: Song Liu
>> Reported-by: Ephraim Park
>> ---
>> kernel/events/core.c | 68
>> +++-
>> 1 file changed, 67 insertions(+), 1 deletion(-)
>>
>> diff --git a/kernel/events/core.c b/kernel/events/core.c
>> index 5789810..623d38f 100644
>> --- a/kernel/events/core.c
>> +++ b/kernel/events/core.c
>
>> @@ -766,6 +821,17 @@ perf_cgroup_set_timestamp(struct task_struct *task,
>> cgrp = perf_cgroup_from_task(task, ctx);
>> info = this_cpu_ptr(cgrp->info);
>> info->timestamp = ctx->timestamp;
>> +
>> +/* set timestamp for ancestor cgroups */
>> +if (cgrp->css.cgroup->level > 1) {
>> +struct perf_cgroup_info *info = this_cpu_ptr(cgrp->info);
>> +struct perf_event *event;
>> +
>> +list_for_each_entry(event, &ctx->pinned_groups, group_entry)
>> +perf_ancestor_cgroup_set_timestamp(event, cgrp, info);
>> +list_for_each_entry(event, &ctx->flexible_groups, group_entry)
>> +perf_ancestor_cgroup_set_timestamp(event, cgrp, info);
>> +}
>> }
>
> That doesn't make any kind of sense... if we're interested in ancestor
> groups, then WTH are you iterating _events_ ?
>
> I'm expecting something like:
>
> struct cgroup_subsys_state *css;
>
> for (css = cgrp->css; css; css = css->parent) {
> /* fudge time */
> }
I guess this is what I have been looking for! Thanks Peter!
V2 coming soon...
Song
Re: [PATCH] perf: update perf_cgroup time for ancestor cgroup(s)
On Sun, Mar 11, 2018 at 10:32:44PM -0700, Song Liu wrote:
> When a perf_event is attached to parent cgroup, it should count events
> for all children cgroups:
>
> parent_group < perf_event
>\
> - child_group < process(es)
>
> However, in our tests, we found this perf_event cannot report reliable
> results. This is because perf_event->cgrp and cpuctx->cgrp are not
> identical, thus perf_event->cgrp are not updated properly.
It might help now and in for our older selves, if you could provide a
simple reproducer for this.
> Signed-off-by: Song Liu
> Reported-by: Ephraim Park
> ---
> kernel/events/core.c | 68
> +++-
> 1 file changed, 67 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 5789810..623d38f 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -766,6 +821,17 @@ perf_cgroup_set_timestamp(struct task_struct *task,
> cgrp = perf_cgroup_from_task(task, ctx);
> info = this_cpu_ptr(cgrp->info);
> info->timestamp = ctx->timestamp;
> +
> + /* set timestamp for ancestor cgroups */
> + if (cgrp->css.cgroup->level > 1) {
> + struct perf_cgroup_info *info = this_cpu_ptr(cgrp->info);
> + struct perf_event *event;
> +
> + list_for_each_entry(event, &ctx->pinned_groups, group_entry)
> + perf_ancestor_cgroup_set_timestamp(event, cgrp, info);
> + list_for_each_entry(event, &ctx->flexible_groups, group_entry)
> + perf_ancestor_cgroup_set_timestamp(event, cgrp, info);
> + }
> }
That doesn't make any kind of sense... if we're interested in ancestor
groups, then WTH are you iterating _events_ ?
I'm expecting something like:
struct cgroup_subsys_state *css;
for (css = cgrp->css; css; css = css->parent) {
/* fudge time */
}
[PATCH] perf: update perf_cgroup time for ancestor cgroup(s)
When a perf_event is attached to parent cgroup, it should count events
for all children cgroups:
parent_group < perf_event
\
- child_group < process(es)
However, in our tests, we found this perf_event cannot report reliable
results. This is because perf_event->cgrp and cpuctx->cgrp are not
identical, thus perf_event->cgrp are not updated properly.
This patch fixes this by updating perf_cgroup properly for ancestor
cgroup(s).
Signed-off-by: Song Liu
Reported-by: Ephraim Park
---
kernel/events/core.c | 68 +++-
1 file changed, 67 insertions(+), 1 deletion(-)
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 5789810..623d38f 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -722,11 +722,48 @@ static inline void __update_cgrp_time(struct perf_cgroup
*cgrp)
info->timestamp = now;
}
+static inline void
+update_ancestor_cgroup_time(struct perf_event *event,
+ struct perf_cgroup *cgrp,
+ struct perf_cgroup_info *cgrp_info)
+{
+ if (!is_cgroup_event(event))
+ return;
+
+ if (cgroup_is_descendant(cgrp->css.cgroup,
+event->cgrp->css.cgroup) &&
+ event->cgrp != cgrp) {
+ struct perf_cgroup_info *info;
+
+ info = this_cpu_ptr(event->cgrp->info);
+ info->time += cgrp_info->timestamp - info->timestamp;
+ info->timestamp = cgrp_info->timestamp;
+ }
+}
+
static inline void update_cgrp_time_from_cpuctx(struct perf_cpu_context
*cpuctx)
{
struct perf_cgroup *cgrp_out = cpuctx->cgrp;
- if (cgrp_out)
+
+ if (cgrp_out) {
__update_cgrp_time(cgrp_out);
+
+ /* update time for ancestor cgroups */
+ if (cgrp_out->css.cgroup->level > 1) {
+ struct perf_cgroup_info *info
+ = this_cpu_ptr(cgrp_out->info);
+ struct perf_event *event;
+
+ list_for_each_entry(event, &cpuctx->ctx.pinned_groups,
+ group_entry)
+ update_ancestor_cgroup_time(event, cgrp_out,
+ info);
+ list_for_each_entry(event, &cpuctx->ctx.flexible_groups,
+ group_entry)
+ update_ancestor_cgroup_time(event, cgrp_out,
+ info);
+ }
+ }
}
static inline void update_cgrp_time_from_event(struct perf_event *event)
@@ -749,6 +786,24 @@ static inline void update_cgrp_time_from_event(struct
perf_event *event)
}
static inline void
+perf_ancestor_cgroup_set_timestamp(struct perf_event *event,
+ struct perf_cgroup *cgrp,
+ struct perf_cgroup_info *cgrp_info)
+{
+ if (!is_cgroup_event(event))
+ return;
+
+ if (cgroup_is_descendant(cgrp->css.cgroup,
+event->cgrp->css.cgroup) &&
+ event->cgrp != cgrp) {
+ struct perf_cgroup_info *info
+ = this_cpu_ptr(event->cgrp->info);
+
+ info->timestamp = cgrp_info->timestamp;
+ }
+}
+
+static inline void
perf_cgroup_set_timestamp(struct task_struct *task,
struct perf_event_context *ctx)
{
@@ -766,6 +821,17 @@ perf_cgroup_set_timestamp(struct task_struct *task,
cgrp = perf_cgroup_from_task(task, ctx);
info = this_cpu_ptr(cgrp->info);
info->timestamp = ctx->timestamp;
+
+ /* set timestamp for ancestor cgroups */
+ if (cgrp->css.cgroup->level > 1) {
+ struct perf_cgroup_info *info = this_cpu_ptr(cgrp->info);
+ struct perf_event *event;
+
+ list_for_each_entry(event, &ctx->pinned_groups, group_entry)
+ perf_ancestor_cgroup_set_timestamp(event, cgrp, info);
+ list_for_each_entry(event, &ctx->flexible_groups, group_entry)
+ perf_ancestor_cgroup_set_timestamp(event, cgrp, info);
+ }
}
static DEFINE_PER_CPU(struct list_head, cgrp_cpuctx_list);
--
2.9.5
