Re: [PATCH v2 0/2] sched/topology: optimize topology_span_sane()

From: Christophe JAILLET
Date: Thu Aug 29 2024 - 02:13:18 EST


Le 28/08/2024 à 16:09, Yury Norov a écrit :
Ping again?


Hi,

The covert letter is v2, but the patch below it are without v2.

In patch 1/2, the Suggested-by: tags in v1 have been removed in this new version :(.

CJ

On Wed, Aug 14, 2024 at 09:35:04AM -0700, Yury Norov wrote:
Ping?

On Wed, Aug 07, 2024 at 12:05:19PM -0700, Yury Norov wrote:
The function may call cpumask_equal with tl->mask(cpu) == tl->mask(i),
even when cpu != i. In such case, cpumask_equal() would always return
true, and we can proceed to the next iteration immediately.

Valentin Schneider shares on it:

PKG can potentially hit that condition, and so can any
sched_domain_mask_f that relies on the node masks...
I'm thinking ideally we should have checks in place to
ensure all node_to_cpumask_map[] masks are disjoint,
then we could entirely skip the levels that use these
masks in topology_span_sane(), but there's unfortunately
no nice way to flag them... Also there would be cases
where there's no real difference between PKG and NODE
other than NODE is still based on a per-cpu cpumask and
PKG isn't, so I don't see a nicer way to go about this.

v1: https://lore.kernel.org/lkml/ZrJk00cmVaUIAr4G@yury-ThinkPad/T/
v2:
- defer initialization of 'mc' in patch #1 @Chen Yu;
- more comments from Valentin Schneider.


Yury Norov (2):
sched/topology: pre-compute topology_span_sane() loop params
sched/topology: optimize topology_span_sane()

kernel/sched/topology.c | 20 ++++++++++++++++++--
1 file changed, 18 insertions(+), 2 deletions(-)

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2.43.0