linux-kernel - Re: [PATCH v2 4/7] sched_ext: Add a DL server for sched

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <aUOpxVIQieTOMifV@jlelli-thinkpadt14gen4.remote.csb>
Date: Thu, 18 Dec 2025 08:14:13 +0100
From: Juri Lelli <juri.lelli@...hat.com>
To: Andrea Righi <arighi@...dia.com>
Cc: Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
	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>, Tejun Heo <tj@...nel.org>,
	David Vernet <void@...ifault.com>,
	Changwoo Min <changwoo@...lia.com>, Shuah Khan <shuah@...nel.org>,
	Joel Fernandes <joelagnelf@...dia.com>,
	Christian Loehle <christian.loehle@....com>,
	Emil Tsalapatis <emil@...alapatis.com>, sched-ext@...ts.linux.dev,
	bpf@...r.kernel.org, linux-kselftest@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/7] sched_ext: Add a DL server for sched_ext tasks

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@....com>
> Co-developed-by: Joel Fernandes <joelagnelf@...dia.com>
> Signed-off-by: Joel Fernandes <joelagnelf@...dia.com>
> Signed-off-by: Andrea Righi <arighi@...dia.com>
> ---

This new version looks good to me, thanks!

Reviewed-by: Juri Lelli <juri.lelli@...hat.com>

Best,
Juri