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Date: Wed, 22 May 2024 09:42:57 +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,
Any chance of getting this in somewhere? I am gradually implementing an
exponential back-off in terms of pinging this thread but it is a simple
and clear improvement so I don't know why it is stuck really.
Kind regards,
Tvrtko
On 01/05/2024 16:09, Tvrtko Ursulin wrote:
>
> 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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