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Date: Wed, 1 May 2024 16:09:50 +0100
From: Tvrtko Ursulin <tvrtko.ursulin@...lia.com>
To: Tvrtko Ursulin <tursulin@...lia.com>
Cc: linux-kernel@...r.kernel.org, Tvrtko Ursulin <tursulin@...ulin.net>,
Suren Baghdasaryan <surenb@...gle.com>, Peter Ziljstra
<peterz@...radead.org>, kernel-dev@...lia.com,
Johannes Weiner <hannes@...xchg.org>, Juri Lelli <juri.lelli@...hat.com>,
Vincent Guittot <vincent.guittot@...aro.org>, Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH] sched/psi: Optimise psi_group_change a bit
Hi,
Adding more scheduler maintainers to Cc - hopefully someone can merge to
the relevant tree?
Thanks,
Tvrtko
On 18/04/2024 09:54, Tvrtko Ursulin wrote:
>
> Hi Ingo,
>
> On 09/04/2024 23:38, Johannes Weiner wrote:
>> [ Oops, I still had an old mutt alias for Ingo's address. ]
>>
>> Ingo, would you mind taking this through the scheduler tree?
>
> Gentle reminder so this one does not fall through the cracks.
>
> Regards,
>
> Tvrtko
>
>> On Fri, Mar 29, 2024 at 02:51:53PM -0400, Johannes Weiner wrote:
>>> On Fri, Mar 29, 2024 at 04:06:48PM +0000, Tvrtko Ursulin wrote:
>>>> From: Tvrtko Ursulin <tursulin@...ulin.net>
>>>>
>>>> The current code loops over the psi_states only to call a helper which
>>>> then resolves back to the action needed for each state using a switch
>>>> statement. That is effectively creating a double indirection of a kind
>>>> which, given how all the states need to be explicitly listed and
>>>> handled
>>>> anyway, we can simply remove. Both the for loop and the switch
>>>> statement
>>>> that is.
>>>>
>>>> The benefit is both in the code size and CPU time spent in this
>>>> function.
>>>> YMMV but on my Steam Deck, while in a game, the patch makes the CPU
>>>> usage
>>>> go from ~2.4% down to ~1.2%. Text size at the same time went from
>>>> 0x323 to
>>>> 0x2c1.
>>>>
>>>> Signed-off-by: Tvrtko Ursulin <tursulin@...ulin.net>
>>>> Cc: Johannes Weiner <hannes@...xchg.org>
>>>> Cc: Suren Baghdasaryan <surenb@...gle.com>
>>>> Cc: Peter Ziljstra <peterz@...radead.org>
>>>> Cc: linux-kernel@...r.kernel.org
>>>> Cc: kernel-dev@...lia.com
>>>
>>> This is great.
>>>
>>> Acked-by: Johannes Weiner <hannes@...xchg.org>
>>>
>>> Ingo, would you mind please taking this through the scheduler tree? I
>>> think Peter is still out.
>>>
>>> Remaining quote below.
>>>
>>> Thanks
>>>
>>>> ---
>>>> kernel/sched/psi.c | 54
>>>> +++++++++++++++++++++++-----------------------
>>>> 1 file changed, 27 insertions(+), 27 deletions(-)
>>>>
>>>> diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
>>>> index 7b4aa5809c0f..55720ecf420e 100644
>>>> --- a/kernel/sched/psi.c
>>>> +++ b/kernel/sched/psi.c
>>>> @@ -218,28 +218,32 @@ void __init psi_init(void)
>>>> group_init(&psi_system);
>>>> }
>>>> -static bool test_state(unsigned int *tasks, enum psi_states state,
>>>> bool oncpu)
>>>> +static u32 test_states(unsigned int *tasks, u32 state_mask)
>>>> {
>>>> - switch (state) {
>>>> - case PSI_IO_SOME:
>>>> - return unlikely(tasks[NR_IOWAIT]);
>>>> - case PSI_IO_FULL:
>>>> - return unlikely(tasks[NR_IOWAIT] && !tasks[NR_RUNNING]);
>>>> - case PSI_MEM_SOME:
>>>> - return unlikely(tasks[NR_MEMSTALL]);
>>>> - case PSI_MEM_FULL:
>>>> - return unlikely(tasks[NR_MEMSTALL] &&
>>>> - tasks[NR_RUNNING] == tasks[NR_MEMSTALL_RUNNING]);
>>>> - case PSI_CPU_SOME:
>>>> - return unlikely(tasks[NR_RUNNING] > oncpu);
>>>> - case PSI_CPU_FULL:
>>>> - return unlikely(tasks[NR_RUNNING] && !oncpu);
>>>> - case PSI_NONIDLE:
>>>> - return tasks[NR_IOWAIT] || tasks[NR_MEMSTALL] ||
>>>> - tasks[NR_RUNNING];
>>>> - default:
>>>> - return false;
>>>> + const bool oncpu = state_mask & PSI_ONCPU;
>>>> +
>>>> + if (tasks[NR_IOWAIT]) {
>>>> + state_mask |= BIT(PSI_IO_SOME);
>>>> + if (!tasks[NR_RUNNING])
>>>> + state_mask |= BIT(PSI_IO_FULL);
>>>> }
>>>> +
>>>> + if (tasks[NR_MEMSTALL]) {
>>>> + state_mask |= BIT(PSI_MEM_SOME);
>>>> + if (tasks[NR_RUNNING] == tasks[NR_MEMSTALL_RUNNING])
>>>> + state_mask |= BIT(PSI_MEM_FULL);
>>>> + }
>>>> +
>>>> + if (tasks[NR_RUNNING] > oncpu)
>>>> + state_mask |= BIT(PSI_CPU_SOME);
>>>> +
>>>> + if (tasks[NR_RUNNING] && !oncpu)
>>>> + state_mask |= BIT(PSI_CPU_FULL);
>>>> +
>>>> + if (tasks[NR_IOWAIT] || tasks[NR_MEMSTALL] || tasks[NR_RUNNING])
>>>> + state_mask |= BIT(PSI_NONIDLE);
>>>> +
>>>> + return state_mask;
>>>> }
>>>> static void get_recent_times(struct psi_group *group, int cpu,
>>>> @@ -770,7 +774,6 @@ static void psi_group_change(struct psi_group
>>>> *group, int cpu,
>>>> {
>>>> struct psi_group_cpu *groupc;
>>>> unsigned int t, m;
>>>> - enum psi_states s;
>>>> u32 state_mask;
>>>> groupc = per_cpu_ptr(group->pcpu, cpu);
>>>> @@ -841,10 +844,7 @@ static void psi_group_change(struct psi_group
>>>> *group, int cpu,
>>>> return;
>>>> }
>>>> - for (s = 0; s < NR_PSI_STATES; s++) {
>>>> - if (test_state(groupc->tasks, s, state_mask & PSI_ONCPU))
>>>> - state_mask |= (1 << s);
>>>> - }
>>>> + state_mask = test_states(groupc->tasks, state_mask);
>>>> /*
>>>> * Since we care about lost potential, a memstall is FULL
>>>> @@ -1194,7 +1194,7 @@ void psi_cgroup_restart(struct psi_group *group)
>>>> /*
>>>> * After we disable psi_group->enabled, we don't actually
>>>> * stop percpu tasks accounting in each psi_group_cpu,
>>>> - * instead only stop test_state() loop, record_times()
>>>> + * instead only stop test_states() loop, record_times()
>>>> * and averaging worker, see psi_group_change() for details.
>>>> *
>>>> * When disable cgroup PSI, this function has nothing to sync
>>>> @@ -1202,7 +1202,7 @@ void psi_cgroup_restart(struct psi_group *group)
>>>> * would see !psi_group->enabled and only do task accounting.
>>>> *
>>>> * When re-enable cgroup PSI, this function use
>>>> psi_group_change()
>>>> - * to get correct state mask from test_state() loop on tasks[],
>>>> + * to get correct state mask from test_states() loop on tasks[],
>>>> * and restart groupc->state_start from now, use .clear = .set
>>>> = 0
>>>> * here since no task status really changed.
>>>> */
>>>> --
>>>> 2.44.0
>>>>
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