linux-kernel - Re: [PATCH 13/14] selftests/sched_ext: Add test for sched_ext dl

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Message-ID: <664c2c34-1514-421f-b3e4-3aec1139f8e3@arm.com>
Date: Mon, 20 Oct 2025 15:21:26 +0100
From: Christian Loehle <christian.loehle@....com>
To: Andrea Righi <arighi@...dia.com>
Cc: Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
 Juri Lelli <juri.lelli@...hat.com>,
 Vincent Guittot <vincent.guittot@...aro.org>,
 Dietmar Eggemann <dietmar.eggemann@....com>,
 Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>,
 Mel Gorman <mgorman@...e.de>, Valentin Schneider <vschneid@...hat.com>,
 Joel Fernandes <joelagnelf@...dia.com>, Tejun Heo <tj@...nel.org>,
 David Vernet <void@...ifault.com>, Changwoo Min <changwoo@...lia.com>,
 Shuah Khan <shuah@...nel.org>, sched-ext@...ts.linux.dev,
 bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 13/14] selftests/sched_ext: Add test for sched_ext
 dl_server

On 10/20/25 14:55, Andrea Righi wrote:
> Hi Christian,
> 
> On Mon, Oct 20, 2025 at 02:26:17PM +0100, Christian Loehle wrote:
>> On 10/17/25 10:26, Andrea Righi wrote:
>>> Add a selftest to validate the correct behavior of the deadline server
>>> for the ext_sched_class.
>>>
>>> [ Joel: Replaced occurences of CFS in the test with EXT. ]
>>>
>>> Co-developed-by: Joel Fernandes <joelagnelf@...dia.com>
>>> Signed-off-by: Joel Fernandes <joelagnelf@...dia.com>
>>> Signed-off-by: Andrea Righi <arighi@...dia.com>
>>> ---
>>>  tools/testing/selftests/sched_ext/Makefile    |   1 +
>>>  .../selftests/sched_ext/rt_stall.bpf.c        |  23 ++
>>>  tools/testing/selftests/sched_ext/rt_stall.c  | 214 ++++++++++++++++++
>>>  3 files changed, 238 insertions(+)
>>>  create mode 100644 tools/testing/selftests/sched_ext/rt_stall.bpf.c
>>>  create mode 100644 tools/testing/selftests/sched_ext/rt_stall.c
>>
>>
>> Does this pass consistently for you?
>> For a loop of 1000 runs I'm getting total runtime numbers for the EXT task of:
>>
>>    0.000 -    0.261 |  (7)
>>    0.261 -    0.522 | ###### (86)
>>    0.522 -    4.437 |  (0)
>>    4.437 -    4.698 |  (1)
>>    4.698 -    4.959 | ################### (257)
>>    4.959 -    5.220 | ################################################## (649)
>>
>> I'll try to see what's going wrong here...
> 
> Is that 1000 runs of total_bw? Yeah, the small ones don't look right at
> all, unless they're caused by some errors in the measurement (or something
> wrong in the test itself). Still better than without the dl_server, but
> it'd be nice to understand what's going on. :)
> 
> I'll try to reproduce that on my side as well.
> 

Yes it's pretty much
for i in $(seq 0 999); do ./runner -t rt_stall ; sleep 10; done

I also tried to increase the runtime of the test, but results look the same so I
assume the DL server isn't running in the fail cases.