linux-kernel - [PATCH 2/3] tools/perf: Fix the nrcpus in perf bench futex to enable the run when all CPU's are not online

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Date: Fri,  7 Jun 2024 10:13:53 +0530
From: Athira Rajeev <atrajeev@...ux.vnet.ibm.com>
To: acme@...nel.org, jolsa@...nel.org, adrian.hunter@...el.com,
        irogers@...gle.com, namhyung@...nel.org
Cc: linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, akanksha@...ux.ibm.com,
        maddy@...ux.ibm.com, atrajeev@...ux.vnet.ibm.com, kjain@...ux.ibm.com,
        disgoel@...ux.vnet.ibm.com
Subject: [PATCH 2/3] tools/perf: Fix the nrcpus in perf bench futex to enable  the run when all CPU's are not online

Perf bench epoll fails as below when attempted to run on
on a powerpc system:

   ./perf bench epoll wait
   Running 'epoll/wait' benchmark:
   Run summary [PID 627653]: 79 threads monitoring on 64 file-descriptors for 8 secs.

   perf: pthread_create: No such file or directory

In the setup where this perf bench was ran, difference was that
partition had 640 CPU's, but not all CPUs were online. 80 CPUs
were online. While creating threads and using epoll_wait , code
sets the affinity using cpumask. The cpumask size used is 80
which is picked from "nrcpus = perf_cpu_map__nr(cpu)". Here the
benchmark reports fail while setting affinity for cpu number which
is greater than 80 or higher, because it attempts to set a bit
position which is not allocated on the cpumask. Fix this by changing
the size of cpumask to number of possible cpus and not the number
of online cpus.

Signed-off-by: Athira Rajeev <atrajeev@...ux.vnet.ibm.com>
---
 tools/perf/bench/epoll-ctl.c  | 2 +-
 tools/perf/bench/epoll-wait.c | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/perf/bench/epoll-ctl.c b/tools/perf/bench/epoll-ctl.c
index d3db73dac66a..d66d852b90e4 100644
--- a/tools/perf/bench/epoll-ctl.c
+++ b/tools/perf/bench/epoll-ctl.c
@@ -232,7 +232,7 @@ static int do_threads(struct worker *worker, struct perf_cpu_map *cpu)
 	if (!noaffinity)
 		pthread_attr_init(&thread_attr);

-	nrcpus = perf_cpu_map__nr(cpu);
+	nrcpus = cpu__max_cpu().cpu;
 	cpuset = CPU_ALLOC(nrcpus);
 	BUG_ON(!cpuset);
 	size = CPU_ALLOC_SIZE(nrcpus);
diff --git a/tools/perf/bench/epoll-wait.c b/tools/perf/bench/epoll-wait.c
index 06bb3187660a..ef5c4257844d 100644
--- a/tools/perf/bench/epoll-wait.c
+++ b/tools/perf/bench/epoll-wait.c
@@ -309,7 +309,7 @@ static int do_threads(struct worker *worker, struct perf_cpu_map *cpu)
 	if (!noaffinity)
 		pthread_attr_init(&thread_attr);

-	nrcpus = perf_cpu_map__nr(cpu);
+	nrcpus = cpu__max_cpu().cpu;
 	cpuset = CPU_ALLOC(nrcpus);
 	BUG_ON(!cpuset);
 	size = CPU_ALLOC_SIZE(nrcpus);
-- 
2.43.0