2023-03-20 09:28:22

by Yue Hu

[permalink] [raw]
Subject: [PATCH] workqueue: Drop the NOT_RUNNING check to flags in worker_{set,clr}_flags

From: Yue Hu <[email protected]>

We know whether the worker flags are belong to WORKER_NOT_RUNNING or not
when we are setting and clearing them. So check the flags not running
related is unnecessary for both the cases.

Currently, worker_{set,clr}_flags() are all used for WORKER_NOT_RUNNING
except for clearing WORKER_IDLE. Let's change to directly clear it
instead. Also, update the comment a little in worker_clr_flags().

Signed-off-by: Yue Hu <[email protected]>
---
kernel/workqueue.c | 17 ++++++++---------
1 file changed, 8 insertions(+), 9 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index de4282736999..c56112cb17c3 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -978,10 +978,8 @@ static inline void worker_set_flags(struct worker *worker, unsigned int flags)
WARN_ON_ONCE(worker->task != current);

/* If transitioning into NOT_RUNNING, adjust nr_running. */
- if ((flags & WORKER_NOT_RUNNING) &&
- !(worker->flags & WORKER_NOT_RUNNING)) {
+ if (!(worker->flags & WORKER_NOT_RUNNING))
pool->nr_running--;
- }

worker->flags |= flags;
}
@@ -1007,12 +1005,11 @@ static inline void worker_clr_flags(struct worker *worker, unsigned int flags)

/*
* If transitioning out of NOT_RUNNING, increment nr_running. Note
- * that the nested NOT_RUNNING is not a noop. NOT_RUNNING is mask
- * of multiple flags, not a single flag.
+ * that NOT_RUNNING is mask of multiple flags, not a single flag.
*/
- if ((flags & WORKER_NOT_RUNNING) && (oflags & WORKER_NOT_RUNNING))
- if (!(worker->flags & WORKER_NOT_RUNNING))
- pool->nr_running++;
+ if ((oflags & WORKER_NOT_RUNNING) &&
+ (!(worker->flags & WORKER_NOT_RUNNING)))
+ pool->nr_running++;
}

/**
@@ -1835,7 +1832,9 @@ static void worker_leave_idle(struct worker *worker)

if (WARN_ON_ONCE(!(worker->flags & WORKER_IDLE)))
return;
- worker_clr_flags(worker, WORKER_IDLE);
+ WARN_ON_ONCE(worker->task != current);
+
+ worker->flags &= ~WORKER_IDLE;
pool->nr_idle--;
list_del_init(&worker->entry);
}
--
2.17.1



2023-03-25 09:33:40

by Lai Jiangshan

[permalink] [raw]
Subject: Re: [PATCH] workqueue: Drop the NOT_RUNNING check to flags in worker_{set,clr}_flags

On Fri, Mar 24, 2023 at 9:58 AM Tejun Heo <[email protected]> wrote:
>
> On Mon, Mar 20, 2023 at 05:26:52PM +0800, Yue Hu wrote:
> > From: Yue Hu <[email protected]>
> >
> > We know whether the worker flags are belong to WORKER_NOT_RUNNING or not
> > when we are setting and clearing them. So check the flags not running
> > related is unnecessary for both the cases.
> >
> > Currently, worker_{set,clr}_flags() are all used for WORKER_NOT_RUNNING
> > except for clearing WORKER_IDLE. Let's change to directly clear it
> > instead. Also, update the comment a little in worker_clr_flags().
>
> I'm not sure this is better. Semantically, the existing code seems clearer
> and less error-prone to me and this isn't gonna make any meaningful perf
> difference. Lai, what do you think?

objdump -DSr kernel/workqueue.o | less

3275: 00 00
3273: R_X86_64_32S current_task
WARN_ON_ONCE(worker->task != current);
3277: 48 39 43 40 cmp %rax,0x40(%rbx)
327b: 0f 85 91 00 00 00 jne 3312 <process_one_work+0x3a2>
!(worker->flags & WORKER_NOT_RUNNING)) {
3281: 8b 43 68 mov 0x68(%rbx),%eax
if ((flags & WORKER_NOT_RUNNING) &&
3284: a9 c8 01 00 00 test $0x1c8,%eax
3289: 75 0b jne 3296 <process_one_work+0x326>
struct worker_pool *pool = worker->pool;
328b: 48 8b 43 48 mov 0x48(%rbx),%rax
pool->nr_running--;
328f: 83 68 20 01 subl $0x1,0x20(%rax)
3293: 8b 43 68 mov 0x68(%rbx),%eax
worker->flags |= flags;
3296: 83 c8 40 or $0x40,%eax
3299: 89 43 68 mov %eax,0x68(%rbx)

It seems the compiler will do the trick. The clearer existing code
seems better.

Thanks
Lai

>
> Thanks.
>
> --
> tejun

2023-03-27 03:04:00

by Yue Hu

[permalink] [raw]
Subject: Re: [PATCH] workqueue: Drop the NOT_RUNNING check to flags in worker_{set,clr}_flags

Hi Tejun, Lai,

On Sat, 25 Mar 2023 17:20:14 +0800
Lai Jiangshan <[email protected]> wrote:

> On Fri, Mar 24, 2023 at 9:58?6?2AM Tejun Heo <[email protected]> wrote:
> >
> > On Mon, Mar 20, 2023 at 05:26:52PM +0800, Yue Hu wrote:
> > > From: Yue Hu <[email protected]>
> > >
> > > We know whether the worker flags are belong to WORKER_NOT_RUNNING or not
> > > when we are setting and clearing them. So check the flags not running
> > > related is unnecessary for both the cases.
> > >
> > > Currently, worker_{set,clr}_flags() are all used for WORKER_NOT_RUNNING
> > > except for clearing WORKER_IDLE. Let's change to directly clear it
> > > instead. Also, update the comment a little in worker_clr_flags().
> >
> > I'm not sure this is better. Semantically, the existing code seems clearer
> > and less error-prone to me and this isn't gonna make any meaningful perf
> > difference. Lai, what do you think?
>
> objdump -DSr kernel/workqueue.o | less
>
> 3275: 00 00
> 3273: R_X86_64_32S current_task
> WARN_ON_ONCE(worker->task != current);
> 3277: 48 39 43 40 cmp %rax,0x40(%rbx)
> 327b: 0f 85 91 00 00 00 jne 3312 <process_one_work+0x3a2>
> !(worker->flags & WORKER_NOT_RUNNING)) {
> 3281: 8b 43 68 mov 0x68(%rbx),%eax
> if ((flags & WORKER_NOT_RUNNING) &&
> 3284: a9 c8 01 00 00 test $0x1c8,%eax
> 3289: 75 0b jne 3296 <process_one_work+0x326>
> struct worker_pool *pool = worker->pool;
> 328b: 48 8b 43 48 mov 0x48(%rbx),%rax
> pool->nr_running--;
> 328f: 83 68 20 01 subl $0x1,0x20(%rax)
> 3293: 8b 43 68 mov 0x68(%rbx),%eax
> worker->flags |= flags;
> 3296: 83 c8 40 or $0x40,%eax
> 3299: 89 43 68 mov %eax,0x68(%rbx)
>
> It seems the compiler will do the trick. The clearer existing code
> seems better.

Thank you for taking time to review the patch.

The `worker_set_flags` has two behaviors. One is set worker flags unconditionally.
Another is to conditionally adjust `nr_running`. I understand the adjustment should be
only for the flags that we set to NOT_RUNNING.

And currently the `worker_set_flags()` is not universally used when setting them, such
as in the case of setting WOKER_IDLE. So, I think this helper is not fulfilling its
responsibility, it is actually just only processing `not_running` state.

If the change is meaningful, maybe it's better to name it as worker_set_not_running_flags()?

Anyway, it is just a minor change.

Thanks.

>
> Thanks
> Lai
>
> >
> > Thanks.
> >
> > --
> > tejun