Hi!
On 17/12/25 22:55, Andrea Righi wrote:
sched_ext currently suffers starvation due to RT. The same workload when converted to EXT can get zero runtime if RT is 100% running, causing EXT processes to stall. Fix it by adding a DL server for EXT.
A kselftest is also included later to confirm that both DL servers are functioning correctly:
# ./runner -t rt_stall ===== START ===== TEST: rt_stall DESCRIPTION: Verify that RT tasks cannot stall SCHED_EXT tasks OUTPUT: TAP version 13 1..1 # Runtime of FAIR task (PID 1511) is 0.250000 seconds # Runtime of RT task (PID 1512) is 4.750000 seconds # FAIR task got 5.00% of total runtime ok 1 PASS: FAIR task got more than 4.00% of runtime TAP version 13 1..1 # Runtime of EXT task (PID 1514) is 0.250000 seconds # Runtime of RT task (PID 1515) is 4.750000 seconds # EXT task got 5.00% of total runtime ok 2 PASS: EXT task got more than 4.00% of runtime TAP version 13 1..1 # Runtime of FAIR task (PID 1517) is 0.250000 seconds # Runtime of RT task (PID 1518) is 4.750000 seconds # FAIR task got 5.00% of total runtime ok 3 PASS: FAIR task got more than 4.00% of runtime TAP version 13 1..1 # Runtime of EXT task (PID 1521) is 0.250000 seconds # Runtime of RT task (PID 1522) is 4.750000 seconds # EXT task got 5.00% of total runtime ok 4 PASS: EXT task got more than 4.00% of runtime ok 1 rt_stall # ===== END =====
v5: - do not restart the EXT server on switch_class() (Juri Lelli) v4: - initialize EXT server bandwidth reservation at init time and always keep it active (Andrea Righi) - check for rq->nr_running == 1 to determine when to account idle time (Juri Lelli) v3: - clarify that fair is not the only dl_server (Juri Lelli) - remove explicit stop to reduce timer reprogramming overhead (Juri Lelli) - do not restart pick_task() when it's invoked by the dl_server (Tejun Heo) - depend on CONFIG_SCHED_CLASS_EXT (Andrea Righi) v2: - drop ->balance() now that pick_task() has an rf argument (Andrea Righi)
Tested-by: Christian Loehle christian.loehle@arm.com Co-developed-by: Joel Fernandes joelagnelf@nvidia.com Signed-off-by: Joel Fernandes joelagnelf@nvidia.com Signed-off-by: Andrea Righi arighi@nvidia.com
This new version looks good to me, thanks!
Reviewed-by: Juri Lelli juri.lelli@redhat.com
Best, Juri