Messages in this thread | | | Date | Mon, 1 May 2023 18:42:55 -0700 | From | Ricardo Neri <> | Subject | Re: [PATCH v4 00/12] sched: Avoid unnecessary migrations within SMT domains |
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On Sat, Apr 29, 2023 at 05:32:19PM +0200, Peter Zijlstra wrote: > On Thu, Apr 06, 2023 at 01:31:36PM -0700, Ricardo Neri wrote: > > Hi, > > > > This is v4 of this series. Previous versions can be found here [1], [2], > > and here [3]. To avoid duplication, I do not include the cover letter of > > the original submission. You can read it in [1]. > > > > This patchset applies cleanly on today's master branch of the tip tree. > > > > Changes since v3: > > > > Nobody liked the proposed changes to the setting of prefer_sibling. > > Instead, I tweaked the solution that Dietmar proposed. Now the busiest > > group, not the local group, determines the setting of prefer_sibling. > > > > Vincent suggested improvements to the logic to decide whether to follow > > asym_packing priorities. Peter suggested to wrap that in a helper function. > > I added sched_use_asym_prio(). > > > > Ionela found that removing SD_ASYM_PACKING from the SMT domain in x86 > > rendered sd_asym_packing NULL in SMT cores. Now highest_flag_domain() > > does not assume that all child domains have the requested flag. > > > > Tim found that asym_active_balance() needs to also check for the idle > > states of the SMT siblings of lb_env::dst_cpu. I added such check. > > > > I wrongly assumed that asym_packing could only be used when the busiest > > group had exactly one busy CPU. This broke asym_packing balancing at the > > DIE domain. I limited this check to balances between cores at the MC > > level. > > > > As per suggestion from Dietmar, I removed sched_asym_smt_can_pull_tasks() > > and placed its logic in sched_asym(). Also, sched_asym() uses > > sched_smt_active() to skip checks when not needed. > > > > I also added a patch from Chen Yu to enable asym_packing balancing in > > Meteor Lake, which has CPUs of different maximum frequency in more than > > one die. > > Is the actual topology of Meteor Lake already public? This patch made me > wonder if we need SCHED_CLUSTER topology in the hybrid_topology thing,
Indeed, Meteor Lake will need SCHED_CLUSTER as does Alder Lake. This is in addition to multi-die support.
> but I can't remember (one of the raisins why the endless calls are such > a frigging waste of time) and I can't seem to find the answer using > Google either. > > > Hopefully, these patches are in sufficiently good shape to be merged? > > Changelogs are very sparse towards the end and I had to reverse engineer > some of it which is a shame. But yeah, on a first reading the code looks > mostly ok. Specifically 8-10 had me WTF a bit and only at 11 did it > start to make a little sense. Mostly they utterly fail to answer the > very fundament "why did you do this" question.
I am sorry changelogs are not sufficiently clear. I thought stating the overall goal in the cover letter was enough. In the future, would you prefer that I repeat the cover letter instead of referring to it? Should individual changelogs state the overall goal?
> > Also, you seem to have forgotten to Cc our friends from IBM such that > they might verify you didn't break their Power7 stuff -- or do you have > a Power7 yourself to verify and forgot to mention that?
I do not have a Power7 system. I did emulate it on an x86 system by setting all cores with identical sg->asym_prefer_cpu. Within, cores, SMT siblings had asymmetric priorities. It was only SMT2, though.
> > > Chen Yu (1): > > x86/sched: Add the SD_ASYM_PACKING flag to the die domain of hybrid > > processors > > > > Ricardo Neri (11): > > sched/fair: Move is_core_idle() out of CONFIG_NUMA > > sched/fair: Only do asym_packing load balancing from fully idle SMT > > cores > > sched/fair: Simplify asym_packing logic for SMT cores > > sched/fair: Let low-priority cores help high-priority busy SMT cores > > sched/fair: Keep a fully_busy SMT sched group as busiest > > sched/fair: Use the busiest group to set prefer_sibling > > sched/fair: Do not even the number of busy CPUs via asym_packing > > sched/topology: Check SDF_SHARED_CHILD in highest_flag_domain() > > sched/topology: Remove SHARED_CHILD from ASYM_PACKING > > x86/sched: Remove SD_ASYM_PACKING from the SMT domain flags > > x86/sched/itmt: Give all SMT siblings of a core the same priority > > > > arch/x86/kernel/itmt.c | 23 +--- > > arch/x86/kernel/smpboot.c | 4 +- > > include/linux/sched/sd_flags.h | 5 +- > > kernel/sched/fair.c | 216 +++++++++++++++++---------------- > > kernel/sched/sched.h | 22 +++- > > 5 files changed, 138 insertions(+), 132 deletions(-) > > I'm going to start to queue this and hopefully push out post -rc1 if > nobody objects.
Thanks! Will it be content for v6.4 or v6.5?
BR, Ricardo
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