Messages in this thread | | | Date | Fri, 3 Mar 2023 11:29:52 +0000 | From | Ionela Voinescu <> | Subject | Re: [PATCH v3 08/10] sched/topology: Remove SHARED_CHILD from ASYM_PACKING |
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Hi Ricardo,
On Monday 06 Feb 2023 at 20:58:36 (-0800), Ricardo Neri wrote: > Only x86 and Power7 use ASYM_PACKING. They use it differently. > > Power7 has cores of equal priority, but the SMT siblings of a core have > different priorities. Parent scheduling domains do not need (nor have) the > ASYM_PACKING flag. SHARED_CHILD is not needed. Using SHARED_PARENT would > cause the topology debug code to complain. > > X86 has cores of different priority, but all the SMT siblings of the core > have equal priority. It needs ASYM_PACKING at the MC level, but not at the > SMT level (it also needs it at upper levels if they have scheduling groups > of different priority). Removing ASYM_PACKING from the SMT domain causes > the topology debug code to complain. > > Remove SHARED_CHILD for now. We still need a topology check that satisfies > both architectures. > > Cc: Ben Segall <bsegall@google.com> > Cc: Daniel Bristot de Oliveira <bristot@redhat.com> > Cc: Dietmar Eggemann <dietmar.eggemann@arm.com> > Cc: Len Brown <len.brown@intel.com> > Cc: Mel Gorman <mgorman@suse.de> > Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com> > Cc: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com> > Cc: Steven Rostedt <rostedt@goodmis.org> > Cc: Tim C. Chen <tim.c.chen@intel.com> > Cc: Valentin Schneider <vschneid@redhat.com> > Cc: x86@kernel.org > Cc: linux-kernel@vger.kernel.org > Suggested-by: Valentin Schneider <vschneid@redhat.com> > Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com> > --- > Changes since v2: > * Introduced this patch. > > Changes since v1: > * N/A > --- > include/linux/sched/sd_flags.h | 5 +---- > 1 file changed, 1 insertion(+), 4 deletions(-) > > diff --git a/include/linux/sched/sd_flags.h b/include/linux/sched/sd_flags.h > index 57bde66d95f7..800238854ba5 100644 > --- a/include/linux/sched/sd_flags.h > +++ b/include/linux/sched/sd_flags.h > @@ -132,12 +132,9 @@ SD_FLAG(SD_SERIALIZE, SDF_SHARED_PARENT | SDF_NEEDS_GROUPS) > /* > * Place busy tasks earlier in the domain > * > - * SHARED_CHILD: Usually set on the SMT level. Technically could be set further > - * up, but currently assumed to be set from the base domain > - * upwards (see update_top_cache_domain()). > * NEEDS_GROUPS: Load balancing flag. > */ > -SD_FLAG(SD_ASYM_PACKING, SDF_SHARED_CHILD | SDF_NEEDS_GROUPS) > +SD_FLAG(SD_ASYM_PACKING, SDF_NEEDS_GROUPS)
While this silences the warning one would have gotten when removing SD_ASYM_PACKING from SMT level, it will still result in sd_asym_packing being NULL for these systems, which breaks nohz balance. That is because highest_flag_domain() still stops searching at the first level without the flag set, in this case SMT, even if levels above have the flag set.
Maybe highest_flag_domain() should be changed to take into account the metadata flags?
Thanks, Ionela.
> > /* > * Prefer to place tasks in a sibling domain > -- > 2.25.1 > >
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