Messages in this thread | | | Date | Tue, 6 Dec 2022 08:17:05 +0000 | Subject | Re: [PATCH v1] Revert "cpufreq: schedutil: Move max CPU capacity to sugov_policy" | From | Lukasz Luba <> |
| |
Hi Viresh,
On 12/5/22 09:18, Viresh Kumar wrote: > Lukasz, > > On 10-11-22, 19:57, Sam Wu wrote: >> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c >> index 9161d1136d01..1207c78f85c1 100644 >> --- a/kernel/sched/cpufreq_schedutil.c >> +++ b/kernel/sched/cpufreq_schedutil.c >> @@ -25,9 +25,6 @@ struct sugov_policy { >> unsigned int next_freq; >> unsigned int cached_raw_freq; >> >> - /* max CPU capacity, which is equal for all CPUs in freq. domain */ >> - unsigned long max; >> - >> /* The next fields are only needed if fast switch cannot be used: */ >> struct irq_work irq_work; >> struct kthread_work work; >> @@ -51,6 +48,7 @@ struct sugov_cpu { >> >> unsigned long util; >> unsigned long bw_dl; >> + unsigned long max; > > IIUC, this part, i.e. moving max to sugov_policy, wasn't the problem > here, right ? Can you send a patch for that at least first, since this > is fully reverted now. > > Or it doesn't make sense? >
Yes, that still could make sense. We could still optimize a bit that code in the sugov_next_freq_shared(). Look at that function. It loops over all CPUs in the policy and calls sugov_get_util() which calls this arch_scale_cpu_capacity() N times. Then it does those multiplications below:
if (j_util * max > j_max * util)
which will be 2*N mul operations... IMO this is pointless and heavy for LITTLE cores which are 4 or sometimes 6 in the policy.
As you could see, my code just left that loop with a simple max() operation.
I might just attack this code differently. Switch to that sugov_policy::max, fetch the cpu capacity only once, before that loop. I will rewrite a bit the sugov_get_util() and adjust the 2nd user of it: sugov_update_single_common()
Regards, Lukasz
| |