linux-kernel - Re: SCHED_DEADLINE tasks missing their deadline with SCHED_FLAG

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 for Android: free password hash cracker in your pocket

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

Message-ID: <aFUwt6ZIO3VbJ1AJ@jlelli-thinkpadt14gen4.remote.csb>
Date: Fri, 20 Jun 2025 11:58:15 +0200
From: Juri Lelli <juri.lelli@...hat.com>
To: luca abeni <luca.abeni@...tannapisa.it>
Cc: Marcel Ziswiler <marcel.ziswiler@...ethink.co.uk>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Vineeth Pillai <vineeth@...byteword.org>
Subject: Re: SCHED_DEADLINE tasks missing their deadline with
 SCHED_FLAG_RECLAIM jobs in the mix (using GRUB)

On 20/06/25 11:37, luca abeni wrote:
> Hi Juri,
> 
> On Fri, 20 Jun 2025 11:29:52 +0200
> Juri Lelli <juri.lelli@...hat.com> wrote:
> [...]
> > I have been playing a little more with this and noticed (by chance)
> > that after writing a value on sched_rt_runtime_us (even the 950000
> > default) this seem to 'work' - I don't see deadline misses anymore.
> > 
> > I thus have moved my attention to GRUB related per-cpu variables [1]
> > and noticed something that looks fishy with extra_bw: after boot and
> > w/o any DEADLINE tasks around (other than dl_servers) all dl_rqs have
> > different values [2]. E.g.,
> > 
> >   extra_bw   : (u64)447170
> >   extra_bw   : (u64)604454
> [...]
> > So, this might be one thing to look at, but I am honestly still
> > confused by why we have weird numbers as the above after boot. Also a
> > bit confused by the actual meaning and purpose of the 5 GRUB
> > variables we have to deal with.
> 
> Sorry about that... I was under the impression they were documented in
> some comments, but I might be wrong...

No worries! I am also culpable, as I did test and review the patches. :)
extra_bw in particular I believe can benefit from a bit of attention.

> > Luca, Vineeth (for the recent introduction of max_bw), maybe we could
> > take a step back and re-check (and maybe and document better :) what
> > each variable is meant to do and how it gets updated?
> 
> I am not sure about the funny values initially assigned to these
> variables, but I can surely provide some documentation about what these
> variables represent... I am going to look at this and I'll send some
> comments or patches.

Thanks a lot! I am also continuing to dig.