[PATCH] selftests/futex_requeue: Increase futex timeout to cover slow hardware

[PATCH] selftests/futex_requeue: Increase futex timeout to cover slow hardware

[Feng Tang]

When running  mixed stress tests (stess-ng, kernel selftests etc.)
on a slow machine, futex 'requeue_multiple' case failed randomly,
with message:
"
    waiter failed errno 110
    not ok 2 futex_requeue many returned: 0 Success
    not ok 3 futex_requeue many returned: 0 Success
    # Planned tests != run tests (2 != 3)
    # Totals: pass:1 fail:2 xfail:0 xpass:0 skip:0 error:0
"

The process of 'requeue_multiple' case will:
* create 10 pthreads with futex (timeout 30 ms)
* wait 10 ms
* start 'futex_cmp_requeue' case

So there is an assumption that the 10 threads can be created in 20 ms,
which is safe enough for normal platforms, while for slow platforms
with stress workload, the creation could take more than 20 ms, and
some futex will timeout and cause the case to fail.

Increasing the timeout to 100 ms to cover slow platforms, which doesn't
hurt normal platforms much.

Signed-off-by: Feng Tang <feng.tang@linux.alibaba.com>
---
 tools/testing/selftests/futex/functional/futex_requeue.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/testing/selftests/futex/functional/futex_requeue.c b/tools/testing/selftests/futex/functional/futex_requeue.c
index dcf0d5f2f312..2df9e8dfb04c 100644
--- a/tools/testing/selftests/futex/functional/futex_requeue.c
+++ b/tools/testing/selftests/futex/functional/futex_requeue.c
@@ -11,7 +11,7 @@
 #include "futextest.h"
 #include "kselftest_harness.h"
 
-#define timeout_ns  30000000
+#define timeout_ns  100000000
 #define WAKE_WAIT_US 10000
 
 volatile futex_t *f1;
-- 
2.43.5

Re: [PATCH] selftests/futex_requeue: Increase futex timeout to cover slow hardware

[Thomas Gleixner]

On Fri, Jul 03 2026 at 11:21, Feng Tang wrote:
> When running  mixed stress tests (stess-ng, kernel selftests etc.)
> on a slow machine, futex 'requeue_multiple' case failed randomly,
> with message:
> "
>     waiter failed errno 110
>     not ok 2 futex_requeue many returned: 0 Success
>     not ok 3 futex_requeue many returned: 0 Success
>     # Planned tests != run tests (2 != 3)
>     # Totals: pass:1 fail:2 xfail:0 xpass:0 skip:0 error:0
> "
>
> The process of 'requeue_multiple' case will:
> * create 10 pthreads with futex (timeout 30 ms)
> * wait 10 ms
> * start 'futex_cmp_requeue' case
>
> So there is an assumption that the 10 threads can be created in 20 ms,
> which is safe enough for normal platforms, while for slow platforms
> with stress workload, the creation could take more than 20 ms, and
> some futex will timeout and cause the case to fail.
>
> Increasing the timeout to 100 ms to cover slow platforms, which doesn't
> hurt normal platforms much.

That's just lame and it hurts because it makes testing slower. If you'd
had taken the time to search LKML for discusssions about this issue then
you'd have noticed that there is work in progress to solve that
properly.

  https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/commit/?h=locking/futex&id=157a9b22ff769e1a657aec6210df3ea896600eec

Thanks,

        tglx

Re: [PATCH] selftests/futex_requeue: Increase futex timeout to cover slow hardware

[Feng Tang]

On Sun, Jul 05, 2026 at 10:04:50PM +0200, Thomas Gleixner wrote:
> On Fri, Jul 03 2026 at 11:21, Feng Tang wrote:
> > When running  mixed stress tests (stess-ng, kernel selftests etc.)
> > on a slow machine, futex 'requeue_multiple' case failed randomly,
> > with message:
> > "
> >     waiter failed errno 110
> >     not ok 2 futex_requeue many returned: 0 Success
> >     not ok 3 futex_requeue many returned: 0 Success
> >     # Planned tests != run tests (2 != 3)
> >     # Totals: pass:1 fail:2 xfail:0 xpass:0 skip:0 error:0
> > "
> >
> > The process of 'requeue_multiple' case will:
> > * create 10 pthreads with futex (timeout 30 ms)
> > * wait 10 ms
> > * start 'futex_cmp_requeue' case
> >
> > So there is an assumption that the 10 threads can be created in 20 ms,
> > which is safe enough for normal platforms, while for slow platforms
> > with stress workload, the creation could take more than 20 ms, and
> > some futex will timeout and cause the case to fail.
> >
> > Increasing the timeout to 100 ms to cover slow platforms, which doesn't
> > hurt normal platforms much.
> 
> That's just lame and it hurts because it makes testing slower. If you'd
> had taken the time to search LKML for discusssions about this issue then
> you'd have noticed that there is work in progress to solve that
> properly.
> 
>   https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/commit/?h=locking/futex&id=157a9b22ff769e1a657aec6210df3ea896600eec

Thanks for the link!

Good to see it merged. Just tried the latest tip tree, and 'futex_requeue'
did pass on our slow platform. (the timeout is now 2 seconds, which should
cover it well).

I know 157a9b22ff76 ("selftests/futex: Use thread synchronization helpers instead of usleep() ")
was merged, but FWIW: 

	Tested-by: Feng Tang <feng.tang@linux.alibaba.com>

Thanks,
Feng