linux-arm-kernel.lists.infradead.org archive mirror
 help / color / mirror / Atom feed
From: Phil Auld <pauld@redhat.com>
To: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: linux-kernel@vger.kernel.org,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Peter Zijlstra <peterz@infradead.org>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] arch/arm64: Fix topology initialization for core scheduling
Date: Tue, 29 Mar 2022 15:50:48 -0400	[thread overview]
Message-ID: <YkNjGOtG6eb4N8mI@lorien.usersys.redhat.com> (raw)
In-Reply-To: <5a5381cd-813d-7cef-9948-01c3e5e910ef@arm.com>

On Tue, Mar 29, 2022 at 08:55:08PM +0200 Dietmar Eggemann wrote:
> On 29/03/2022 17:20, Phil Auld wrote:
> > On Tue, Mar 29, 2022 at 04:02:22PM +0200 Dietmar Eggemann wrote:
> >> On 22/03/2022 17:03, Phil Auld wrote:
> 
> [...]
> 
> >> I assume this is for a machine which relies on MPIDR-based setup
> >> (package_id == -1)? I.e. it doesn't have proper ACPI/(DT) data for
> >> topology setup.
> > 
> > Yes, that's my understanding. No PPTT.
> > 
> >>
> >> Tried on a ThunderX2 by disabling parse_acpi_topology() but then I end
> >> up with a machine w/o SMT, so `stress-ng --prctl N` doesn't show this issue.
> >>
> >> Which machine were you using?
> > 
> > This instance is an HPE Apollo 70 set to smt-4.  I believe it's ThunderX2
> > chips.
> > 
> > ARM (CN9980-2200LG4077-Y21-G) 
> I'm using the same processor just with ACPI/PPTT.
>

Maybe I'm misinformed about these systems having no PPTT...  

I'm reclaiming the system. Is there a way I can tell from userspace?


> # sudo dmidecode -t 4 | grep "Part Number"
> 	Part Number: CN9980-2200LG4077-21-Y-G
> 	Part Number: CN9980-2200LG4077-21-Y-G
> 
> # cat /sys/devices/system/cpu/cpu0/topology/thread_siblings
> 0,32,64,96
> 
> # cat /sys/kernel/debug/sched/domains/cpu0/domain*/name
> SMT
> MC
> NUMA
> 
> But no matter whether I disable parse_acpi_topology() or just force
> `cpu_topology[cpu].package_id = -1` in this function, I always end up with:
> 
> # cat /sys/kernel/debug/sched/domains/cpu0/domain*/name
> MC
> NUMA
> 
> # cat /sys/devices/system/cpu/cpu0/topology/thread_siblings_list
> 0
> 
> so no SMT sched domain. The MPIDR-based topology fallback code in
> store_cpu_topology() forces `cpuid_topo->thread_id  = -1`.

Right. So since I'm getting SMT it must not have package_id == -1.
In which case you should be able to reproduce it because it must
be that the call the update_siblings_masks() is required.  That
appears to only be called from store_cpu_topology() which is
after the scheduler has already setup the core pointers.

The fix could be the same but I should reword the commit message
since it should effect all SMT arm systems I'd think.

Or maybe the ACPI topology code should call update_sibling_masks().


> 
> IMHO this is why on my machine I don't see this issue while running:
> 
> root@oss-apollo7007:~# stress-ng --prctl 256 -t 60
> stress-ng: info:  [2388042] dispatching hogs: 256 prctl
> 
> Is there something I miss in my setup to provoke this issue?
>

Make sure you have a stress-ng that is new enough and built against
headers that have the CORE_SCHED prctls defined.


BTW, thanks for taking a look.


Cheers,
Phil

> [...]
> 

-- 


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  reply	other threads:[~2022-03-29 19:52 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-03-22 16:03 [PATCH] arch/arm64: Fix topology initialization for core scheduling Phil Auld
2022-03-29 14:02 ` Dietmar Eggemann
2022-03-29 15:20   ` Phil Auld
2022-03-29 18:55     ` Dietmar Eggemann
2022-03-29 19:50       ` Phil Auld [this message]
2022-03-30 15:48         ` Dietmar Eggemann
2022-03-30 15:52           ` Phil Auld
2022-03-30 16:07           ` Phil Auld

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=YkNjGOtG6eb4N8mI@lorien.usersys.redhat.com \
    --to=pauld@redhat.com \
    --cc=catalin.marinas@arm.com \
    --cc=dietmar.eggemann@arm.com \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mark.rutland@arm.com \
    --cc=peterz@infradead.org \
    --cc=will@kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).