linux.git/kernel/sched/psi.c, branch v6.11

Merge branch 'sched/urgent' into sched/core, to pick up fixes and refresh the branch

2024-07-11T08:42:33+00:00

Signed-off-by: Ingo Molnar

sched/psi: Optimise psi_group_change a bit

2024-07-04T13:59:52+00:00

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 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Chengming Zhou 
Acked-by: Johannes Weiner 
Link: https://lkml.kernel.org/r/20240625135000.38652-1-tursulin@igalia.com

sched: Move psi_account_irqtime() out of update_rq_clock_task() hotpath

2024-07-01T11:01:44+00:00

It was reported that in moving to 6.1, a larger then 10%
regression was seen in the performance of
clock_gettime(CLOCK_THREAD_CPUTIME_ID,...).

Using a simple reproducer, I found:
5.10:
100000000 calls in 24345994193 ns => 243.460 ns per call
100000000 calls in 24288172050 ns => 242.882 ns per call
100000000 calls in 24289135225 ns => 242.891 ns per call

6.1:
100000000 calls in 28248646742 ns => 282.486 ns per call
100000000 calls in 28227055067 ns => 282.271 ns per call
100000000 calls in 28177471287 ns => 281.775 ns per call

The cause of this was finally narrowed down to the addition of
psi_account_irqtime() in update_rq_clock_task(), in commit
52b1364ba0b1 ("sched/psi: Add PSI_IRQ to track IRQ/SOFTIRQ
pressure").

In my initial attempt to resolve this, I leaned towards moving
all accounting work out of the clock_gettime() call path, but it
wasn't very pretty, so it will have to wait for a later deeper
rework. Instead, Peter shared this approach:

Rework psi_account_irqtime() to use its own psi_irq_time base
for accounting, and move it out of the hotpath, calling it
instead from sched_tick() and __schedule().

In testing this, we found the importance of ensuring
psi_account_irqtime() is run under the rq_lock, which Johannes
Weiner helpfully explained, so also add some lockdep annotations
to make that requirement clear.

With this change the performance is back in-line with 5.10:
6.1+fix:
100000000 calls in 24297324597 ns => 242.973 ns per call
100000000 calls in 24318869234 ns => 243.189 ns per call
100000000 calls in 24291564588 ns => 242.916 ns per call

Reported-by: Jimmy Shiu 
Originally-by: Peter Zijlstra 
Signed-off-by: John Stultz 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Chengming Zhou 
Reviewed-by: Qais Yousef 
Link: https://lore.kernel.org/r/20240618215909.4099720-1-jstultz@google.com

sched: Fix spelling in comments

2024-05-27T15:00:21+00:00

Do a spell-checking pass.

Signed-off-by: Ingo Molnar 
Cc: Peter Zijlstra 
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar

sched/psi: Update poll => rtpoll in relevant comments

2023-10-16T11:42:49+00:00

The PSI trigger code is now making a distinction between privileged and
unprivileged triggers, after the following commit:

 65457b74aa94 ("sched/psi: Rename existing poll members in preparation")

But some comments have not been modified along with the code, so they
need to be updated.

This will help readers better understand the code.

Signed-off-by: Fan Yu 
Signed-off-by: Ingo Molnar 
Cc: Johannes Weiner 
Cc: Suren Baghdasaryan 
Cc: Peter Ziljstra 
Link: https://lore.kernel.org/r/202310161920399921184@zte.com.cn

sched/psi: Bail out early from irq time accounting

2023-10-13T07:56:29+00:00

We could bail out early when psi was disabled.

Signed-off-by: Haifeng Xu 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Chengming Zhou 
Link: https://lore.kernel.org/r/20230926115722.467833-1-haifeng.xu@shopee.com

sched/psi: Delete the 'update_total' function parameter from update_triggers()

2023-10-11T21:08:09+00:00

The 'update_total' parameter of update_triggers() is always true after the
previous commit:

  80cc1d1d5ee3 ("sched/psi: Avoid updating PSI triggers and ->rtpoll_total when there are no state changes")

If the 'changed_states & group->rtpoll_states' condition is true,
'new_stall' in update_triggers() will be true, and then 'update_total'
should also be true.

So update_total is redundant - remove it.

[ mingo: Changelog updates ]

Signed-off-by: Yang Yang 
Signed-off-by: Ingo Molnar 
Cc: Johannes Weiner 
Cc: Suren Baghdasaryan 
Cc: Peter Ziljstra 
Link: https://lore.kernel.org/r/202310101645437859599@zte.com.cn

sched/psi: Avoid updating PSI triggers and ->rtpoll_total when there are no state changes

2023-10-11T21:07:50+00:00

When psimon wakes up and there are no state changes for ->rtpoll_states,
it's unnecessary to update triggers and ->rtpoll_total because the pressures
being monitored by the user have not changed.

This will help to slightly reduce unnecessary computations of PSI.

[ mingo: Changelog updates ]

Signed-off-by: Yang Yang 
Signed-off-by: Ingo Molnar 
Cc: Johannes Weiner 
Cc: Suren Baghdasaryan 
Cc: Peter Ziljstra 
Link: https://lore.kernel.org/r/202310101641075436843@zte.com.cn

sched/psi: Change update_triggers() to a 'void' function

2023-10-09T12:54:50+00:00

Update_triggers() always returns now + group->rtpoll_min_period, and the
return value is only used by psi_rtpoll_work(), so change update_triggers()
to a void function, let group->rtpoll_next_update = now +
group->rtpoll_min_period directly.

This will avoid unnecessary function return value passing & simplifies
the function.

[ mingo: Updated changelog ]

Suggested-by: Suren Baghdasaryan 
Signed-off-by: Yang Yang 
Signed-off-by: Ingo Molnar 
Link: https://lore.kernel.org/r/202310092024289721617@zte.com.cn

Merge tag 'v6.5-rc2' into sched/core, to pick up fixes

2023-07-19T07:43:25+00:00

Sync with upstream fixes before applying EEVDF.

Signed-off-by: Ingo Molnar