[PATCH] selftests/sched_ext: Fix build error in dequeue_remote selftest

[PATCH] selftests/sched_ext: Fix build error in dequeue_remote selftest

[Samuele Mariotti]

Building the dequeue_remote selftest with newer compilers (e.g., gcc 16)
triggers the following error:

dequeue_remote.c:39:32: error: variable ‘sum’ set but not used

The 'volatile' qualifier prevents the writes from being optimized away,
but does not silence the warning, since 'sum' is indeed only written and
never read.

Consume 'sum' via an empty asm() with a register input constraint, as
already done for the dequeue selftest in commit 3788e3251653
("selftests/sched_ext: Fix build error in dequeue selftest"). This forces
the compiler to keep the accumulated value (preserving the CPU stress loop)
and avoids the build error.

Fixes: cc07fae1de5d ("selftests/sched_ext: Add a test for ops.dequeue() on remote local DSQ moves")

Signed-off-by: Samuele Mariotti <smariotti@disroot.org>
---
 tools/testing/selftests/sched_ext/dequeue_remote.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tools/testing/selftests/sched_ext/dequeue_remote.c b/tools/testing/selftests/sched_ext/dequeue_remote.c
index f2c1901030de..af344581d5f1 100644
--- a/tools/testing/selftests/sched_ext/dequeue_remote.c
+++ b/tools/testing/selftests/sched_ext/dequeue_remote.c
@@ -43,6 +43,7 @@ static void worker_fn(int id)
 
 		for (j = 0; j < 20000 + id * 1000; j++)
 			sum += j;
+		asm volatile("" : : "r"(sum));
 		if (id & 1)
 			usleep(100);
 		else
-- 
2.56.0

Re: [PATCH] selftests/sched_ext: Fix build error in dequeue_remote selftest

[Kuba Piecuch]

On Mon Oct 12, 2026 at 11:59 AM UTC, Samuele Mariotti wrote:
> Building the dequeue_remote selftest with newer compilers (e.g., gcc 16)
> triggers the following error:
>
> dequeue_remote.c:39:32: error: variable ‘sum’ set but not used
>
> The 'volatile' qualifier prevents the writes from being optimized away,
> but does not silence the warning, since 'sum' is indeed only written and
> never read.
>
> Consume 'sum' via an empty asm() with a register input constraint, as
> already done for the dequeue selftest in commit 3788e3251653
> ("selftests/sched_ext: Fix build error in dequeue selftest"). This forces
> the compiler to keep the accumulated value (preserving the CPU stress loop)
> and avoids the build error.
>
> Fixes: cc07fae1de5d ("selftests/sched_ext: Add a test for ops.dequeue() on remote local DSQ moves")
>
> Signed-off-by: Samuele Mariotti <smariotti@disroot.org>
> ---
>  tools/testing/selftests/sched_ext/dequeue_remote.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/tools/testing/selftests/sched_ext/dequeue_remote.c b/tools/testing/selftests/sched_ext/dequeue_remote.c
> index f2c1901030de..af344581d5f1 100644
> --- a/tools/testing/selftests/sched_ext/dequeue_remote.c
> +++ b/tools/testing/selftests/sched_ext/dequeue_remote.c
> @@ -43,6 +43,7 @@ static void worker_fn(int id)
>  
>  		for (j = 0; j < 20000 + id * 1000; j++)
>  			sum += j;
> +		asm volatile("" : : "r"(sum));
>  		if (id & 1)
>  			usleep(100);
>  		else

LGTM, thank you Samuele!

Reviewed-by: Kuba Piecuch <jpiecuch@google.com>

Re: [PATCH] selftests/sched_ext: Fix build error in dequeue_remote selftest

[Tejun Heo]

Applied to sched_ext/for-7.4 with the Fixes tag dropped and the following
tag added:

    Reviewed-by: Kuba Piecuch <jpiecuch@google.com>

Thanks.

--
tejun