linux-kernel - Re: question on sched-rt group allocation cap: sched_rt_runtime

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-next>] [day] [month] [year] [list]

Date:	Sat, 5 Sep 2009 19:32:31 -0700 (PDT)
From:	Ani <asinha@...gmasystems.com>
To:	Lucas De Marchi <lucas.de.marchi@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: question on sched-rt group allocation cap: sched_rt_runtime_us

On Sep 5, 3:50 pm, Lucas De Marchi <lucas.de.mar...@...il.com> wrote:
>
> Indeed. I've tested this same test program in a single core machine and it
> produces the expected behavior:
>
> rt_runtime_us / rt_period_us     % loops executed in SCHED_OTHER
> 95%                              4.48%
> 60%                              54.84%
> 50%                              86.03%
> 40%                              OTHER completed first
>

Hmm. This does seem to indicate that there is some kind of
relationship with SMP. So I wonder whether there is a way to turn this
'RT bandwidth accumulation' heuristic off. I did an
echo 0 > /proc/sys/kernel/sched_migration_cost
but results were identical to previous.

I figure that if I set it to zero, the regular sched-fair (non-RT)
tasks will be treated as not being cache hot and hence susceptible to
migration. From the code it looks like sched-rt tasks are always
treated as cache cold? Mind you though that I have not yet looked into
the code very rigorously. I knew the O(1) scheduler relatively well,
but I am just begun digging into the new CFS scheduler code.

On a side note, why is there no documentation explain the
sched_migration_cost tuning knob? It would be nice to have one - at
least where the sysctl variable is defined.

--Ani
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/