Re: [PATCH V2 22/23] perf tools: Allow system-wide events to keep their own CPUs
From: Liang, Kan
Date: Fri May 13 2022 - 13:32:51 EST
On 5/13/2022 12:42 PM, Namhyung Kim wrote:
On Fri, May 13, 2022 at 9:11 AM Adrian Hunter <adrian.hunter@xxxxxxxxx> wrote:
On 13/05/22 18:46, Liang, Kan wrote:
On 5/13/2022 11:21 AM, Adrian Hunter wrote:
On 13/05/22 17:12, Liang, Kan wrote:
On 5/13/2022 12:48 AM, Adrian Hunter wrote:
On 12/05/22 21:53, Namhyung Kim wrote:
On Thu, May 12, 2022 at 3:35 AM Adrian Hunter <adrian.hunter@xxxxxxxxx> wrote:
On 12/05/22 08:27, Namhyung Kim wrote:
On Fri, May 6, 2022 at 5:27 AM Adrian Hunter <adrian.hunter@xxxxxxxxx> wrote:
Currently, user_requested_cpus supplants system-wide CPUs when the evlist
has_user_cpus. Change that so that system-wide events retain their own
CPUs and they are added to all_cpus.
Acked-by: Ian Rogers <irogers@xxxxxxxxxx>
Signed-off-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>
---
tools/lib/perf/evlist.c | 11 +++++------
1 file changed, 5 insertions(+), 6 deletions(-)
diff --git a/tools/lib/perf/evlist.c b/tools/lib/perf/evlist.c
index 1c801f8da44f..9a6801b53274 100644
--- a/tools/lib/perf/evlist.c
+++ b/tools/lib/perf/evlist.c
@@ -40,12 +40,11 @@ static void __perf_evlist__propagate_maps(struct perf_evlist *evlist,
* We already have cpus for evsel (via PMU sysfs) so
* keep it, if there's no target cpu list defined.
*/
- if (!evsel->own_cpus || evlist->has_user_cpus) {
- perf_cpu_map__put(evsel->cpus);
- evsel->cpus = perf_cpu_map__get(evlist->user_requested_cpus);
- } else if (!evsel->system_wide &&
- !evsel->requires_cpu &&
- perf_cpu_map__empty(evlist->user_requested_cpus)) {
+ if (!evsel->own_cpus ||
+ (!evsel->system_wide && evlist->has_user_cpus) ||
+ (!evsel->system_wide &&
+ !evsel->requires_cpu &&
+ perf_cpu_map__empty(evlist->user_requested_cpus))) {
This is getting hard to understand. IIUC this propagation basically
sets user requested cpus to evsel unless it has its own cpus, right?
I put the conditional logic altogether because that is kernel style but
it does make it practically unreadable.
If we start with the original logic:
if (!evsel->own_cpus || evlist->has_user_cpus) {
perf_cpu_map__put(evsel->cpus);
evsel->cpus = perf_cpu_map__get(evlist->user_requested_cpus);
} else if (!evsel->system_wide && perf_cpu_map__empty(evlist->user_requested_cpus)) {
perf_cpu_map__put(evsel->cpus);
evsel->cpus = perf_cpu_map__get(evlist->user_requested_cpus);
} else if (evsel->cpus != evsel->own_cpus) {
perf_cpu_map__put(evsel->cpus);
evsel->cpus = perf_cpu_map__get(evsel->own_cpus);
}
Then make it more readable, i.e. same functionality
struct perf_cpu_map *cpus;
if (!evsel->own_cpus || evlist->has_user_cpus)
cpus = evlist->user_requested_cpus;
else if (!evsel->system_wide && perf_cpu_map__empty(evlist->user_requested_cpus))
cpus = evlist->user_requested_cpus;
else
cpus = evsel->own_cpus;
if (evsel->cpus != cpus) {
perf_cpu_map__put(evsel->cpus);
evsel->cpus = perf_cpu_map__get(cpus);
}
Then separate out the conditions, i.e. still same functionality
if (!evsel->own_cpus)
cpus = evlist->user_requested_cpus;
else if (evlist->has_user_cpus)
cpus = evlist->user_requested_cpus;
else if (evsel->system_wide)
cpus = evsel->own_cpus;
else if (perf_cpu_map__empty(evlist->user_requested_cpus)) /* per-thread */
cpus = evlist->user_requested_cpus;
else
cpus = evsel->own_cpus;
Then add the new requires_cpu flag:
if (!evsel->own_cpus)
cpus = evlist->user_requested_cpus;
else if (evlist->has_user_cpus)
cpus = evlist->user_requested_cpus;
else if (evsel->system_wide)
cpus = evsel->own_cpus;
- else if (perf_cpu_map__empty(evlist->user_requested_cpus)) /* per-thread */
+ else if (!evsel->requres_cpu && perf_cpu_map__empty(evlist->user_requested_cpus)) /* per-thread */
cpus = evlist->user_requested_cpus;
else
cpus = evsel->own_cpus;
Then make system_wide keep own_cpus even if has_user_cpus:
if (!evsel->own_cpus)
cpus = evlist->user_requested_cpus;
+ else if (evsel->system_wide)
+ cpus = evsel->own_cpus;
else if (evlist->has_user_cpus)
cpus = evlist->user_requested_cpus;
- else if (evsel->system_wide)
- cpus = evsel->own_cpus;
else if (!evsel->requres_cpu && perf_cpu_map__empty(evlist->user_requested_cpus)) /* per-thread */
cpus = evlist->user_requested_cpus;
else
cpus = evsel->own_cpus;
Which leaves:
if (!evsel->own_cpus)
cpus = evlist->user_requested_cpus;
else if (evsel->system_wide)
cpus = evsel->own_cpus;
else if (evlist->has_user_cpus)
cpus = evlist->user_requested_cpus;
else if (!evsel->requres_cpu && perf_cpu_map__empty(evlist->user_requested_cpus)) /* per-thread */
cpus = evlist->user_requested_cpus;
else
cpus = evsel->own_cpus;
And putting it back together:
if (!evsel->own_cpus ||
(!evsel->system_wide && evlist->has_user_cpus) ||
(!evsel->system_wide &&
!evsel->requires_cpu &&
perf_cpu_map__empty(evlist->user_requested_cpus))) {
cpus = evlist->user_requested_cpus;
else
cpus = evsel->own_cpus;
Perhaps I shouldn't put it together?
Cool, thanks a lot for explaining it in detail.
I do not oppose your change but little worried about the
complexity. And I think we have some issues with uncore
events already.
Yes it is a bit complicated because we are handling
many different use cases.
So do you have any idea where evsel->own_cpus
doesn't propagate to evsel->cpus?
We let the user's list of CPUs override it i.e. the
evlist->has_user_cpus case. Essentially we are expecting
the user to know what they are doing.
I think evsel->system_wide and evsel->requires_cpu
can be replaced to check evsel->own_cpus instead.
Not at the moment because we let the user override
own_cpus.
Do we check whether the user's input is valid (match the PMU's cpumask) before the override?
I think we know the PMU name. The cpumask of the PMU can be found in the sysfs. So we should have enough information for a sanity check.
For the uncore PMU case, I am not sure what sanity is :-)
For a non-core PMU, e.g., uncore, cstate, power and etc. The cpumask is under the /sys/devices/<PMU>/cpumask. It shows the cpumask which kernel supports. If a end user request a different CPU other that the cpumask, I think it's better throw a waning. It should mitigate the confusion which Namhyung mentioned (uncore -C1,2).
So you couldn't get uncore events unless you are also coincidentally wanting to trace CPU 0.
I guess really the requrement is not to perf_event_open() an uncore PMU more than once?
To figure that out we'd need to be able map CPUs to uncore PMUs?
We might just use evsel->own_cpus for uncore events and
if the user-given cpu list contains other cpus it can show an
warning.
Yes, it sounds reasonable.
Thanks,
Kan