Messages in this thread | | | Date | Sun, 4 Sep 2022 12:44:36 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH v3 3/6] sched: Change wait_task_inactive()s match_state |
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* Peter Zijlstra <peterz@infradead.org> wrote:
> Make wait_task_inactive()'s @match_state work like ttwu()'s @state. > > That is, instead of an equal comparison, use it as a mask. This allows > matching multiple block conditions. > > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> > --- > kernel/sched/core.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -3295,7 +3295,7 @@ unsigned long wait_task_inactive(struct > * is actually now running somewhere else! > */ > while (task_running(rq, p)) { > - if (match_state && unlikely(READ_ONCE(p->__state) != match_state)) > + if (match_state && !(READ_ONCE(p->__state) & match_state)) > return 0;
We lose the unlikely annotation there - but I guess it probably never really mattered anyway?
Suggestion #1:
- Shouldn't we rename task_running() to something like task_on_cpu()? The task_running() primitive is similar to TASK_RUNNING but is not based off any TASK_FLAGS.
Suggestion #2:
- Shouldn't we eventually standardize on task->on_cpu on UP kernels too? They don't really matter anymore, and doing so removes #ifdefs and makes the code easier to read.
> cpu_relax(); > } > @@ -3310,7 +3310,7 @@ unsigned long wait_task_inactive(struct > running = task_running(rq, p); > queued = task_on_rq_queued(p); > ncsw = 0; > - if (!match_state || READ_ONCE(p->__state) == match_state) > + if (!match_state || (READ_ONCE(p->__state) & match_state)) > ncsw = p->nvcsw | LONG_MIN; /* sets MSB */ > task_rq_unlock(rq, p, &rf);
Suggestion #3:
- Couldn't the following users with a 0 mask:
drivers/powercap/idle_inject.c: wait_task_inactive(iit->tsk, 0); fs/coredump.c: wait_task_inactive(ptr->task, 0);
Use ~0 instead (exposed as TASK_ANY or so) and then we can drop the !match_state special case?
They'd do something like:
drivers/powercap/idle_inject.c: wait_task_inactive(iit->tsk, TASK_ANY); fs/coredump.c: wait_task_inactive(ptr->task, TASK_ANY);
It's not an entirely 100% equivalent transformation though, but looks OK at first sight: ->__state will be some nonzero mask for genuine tasks waiting to schedule out, so any match will be functionally the same as a 0 flag telling us not to check any of the bits, right? I might be missing something though.
Thanks,
Ingo
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