Messages in this thread | | | Date | Mon, 6 Mar 2023 13:10:37 +0000 | From | Ionela Voinescu <> | Subject | Re: [PATCH v3 08/10] sched/topology: Remove SHARED_CHILD from ASYM_PACKING |
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Hey,
On Sunday 05 Mar 2023 at 11:08:11 (-0800), Ricardo Neri wrote: > On Fri, Mar 03, 2023 at 11:29:52AM +0000, Ionela Voinescu wrote: > > Hi Ricardo, > > Hi Ionela! > > > > > 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. > > You are absolutely right! This how this whole discussion started. It > slipped my mind. > > > > > Maybe highest_flag_domain() should be changed to take into account the > > metadata flags? > > What about the patch below? Search will stop if the flag has > SDF_SHARED_CHILD as it does today. Otherwise it will search all the > domains. > > --- a/kernel/sched/sched.h > +++ b/kernel/sched/sched.h > @@ -1773,6 +1773,12 @@ queue_balance_callback(struct rq *rq, > for (__sd = rcu_dereference_check_sched_domain(cpu_rq(cpu)->sd); \ > __sd; __sd = __sd->parent) > > +#define SD_FLAG(name, mflags) (name * !!((mflags) & SDF_SHARED_CHILD)) | > +static const unsigned int SD_SHARED_CHILD_MASK = > +#include <linux/sched/sd_flags.h> > +0; > +#undef SD_FLAG > + > /** > * highest_flag_domain - Return highest sched_domain containing flag. > * @cpu: The CPU whose highest level of sched domain is to > @@ -1781,15 +1787,19 @@ queue_balance_callback(struct rq *rq, > * for the given CPU. > * > * Returns the highest sched_domain of a CPU which contains the given flag. > - */ > +*/ ^^^ likely an unintended change > static inline struct sched_domain *highest_flag_domain(int cpu, int flag) > { > struct sched_domain *sd, *hsd = NULL; > > for_each_domain(cpu, sd) { > - if (!(sd->flags & flag)) > + if (sd->flags & flag) { > + hsd = sd; > + continue; > + } > +
There might be room for a comment here: /* * If the flag is not set and is known to be shared with lower * domains, stop the search, as it won't be found further up. */ > + if (flag & SD_SHARED_CHILD_MASK) > break; > - hsd = sd; > } > > return hsd;
It looks nice and sane to me - I've not compiled or tested it :).
Thanks, Ionela.
> > > > > Thanks, > > Ionela. > > > > > > > > /* > > > * Prefer to place tasks in a sibling domain > > > -- > > > 2.25.1 > > > > > >
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