Messages in this thread | | | Date | Tue, 12 Dec 2023 09:04:19 -0800 | From | Yury Norov <> | Subject | Re: [PATCH v3 2/7] lib/group_cpus: optimize inner loop in grp_spread_init_one() |
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On Tue, Dec 12, 2023 at 05:46:53PM +0800, Ming Lei wrote: > On Mon, Dec 11, 2023 at 08:21:02PM -0800, Yury Norov wrote: > > The loop starts from the beginning every time we switch to the next > > sibling mask. This is the Schlemiel the Painter's style of coding > > because we know for sure that nmsk is clear up to current CPU, and we > > can just continue from the next CPU. > > > > Also, we can do it nicer if leverage the dedicated for_each() iterator, > > and simplify the logic of clearing a bit in nmsk. > > > > Signed-off-by: Yury Norov <yury.norov@gmail.com> > > --- > > lib/group_cpus.c | 13 ++++++------- > > 1 file changed, 6 insertions(+), 7 deletions(-) > > > > diff --git a/lib/group_cpus.c b/lib/group_cpus.c > > index ee272c4cefcc..10dead3ab0e0 100644 > > --- a/lib/group_cpus.c > > +++ b/lib/group_cpus.c > > @@ -30,14 +30,13 @@ static void grp_spread_init_one(struct cpumask *irqmsk, struct cpumask *nmsk, > > > > /* If the cpu has siblings, use them first */ > > siblmsk = topology_sibling_cpumask(cpu); > > - for (sibl = -1; cpus_per_grp > 0; ) { > > - sibl = cpumask_next(sibl, siblmsk); > > - if (sibl >= nr_cpu_ids) > > - break; > > - if (!cpumask_test_and_clear_cpu(sibl, nmsk)) > > - continue; > > + sibl = cpu + 1; > > It doesn't have to 'cpu + 1', see below comment. > > > + > > + for_each_cpu_and_from(sibl, siblmsk, nmsk) { > > + cpumask_clear_cpu(sibl, nmsk); > > cpumask_set_cpu(sibl, irqmsk); > > - cpus_per_grp--; > > + if (cpus_per_grp-- == 0) > > if (--cpus_per_grp == 0)
That's right, I'll send a new version this weekend.
> > + return; > > I think for_each_cpu_and() should work just fine, cause cpu has been cleared > from nmsk, so the change can be something like, then patch 1 isn't > necessary.
It works just fine except that it's O(N^2), where O(N) is easily achievable. Again, it's not about performance, it's about coding habits.
> for_each_cpu_and(sibl, siblmsk, nmsk) { > cpumask_clear_cpu(sibl, nmsk); > cpumask_set_cpu(sibl, irqmsk); > if (--cpus_per_grp == 0) > return; > } > > > Thanks, > Ming
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