From: Jason Baron <jbaron@akamai.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: mingo@redhat.com, viro@zeniv.linux.org.uk,
akpm@linux-foundation.org, normalperson@yhbt.net,
davidel@xmailserver.org, mtk.manpages@gmail.com,
linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 1/2] sched/wait: add round robin wakeup mode
Date: Tue, 10 Feb 2015 10:59:01 -0500 [thread overview]
Message-ID: <54DA2AC5.6020508@akamai.com> (raw)
In-Reply-To: <20150210090336.GV21418@twins.programming.kicks-ass.net>
On 02/10/2015 04:03 AM, Peter Zijlstra wrote:
> On Mon, Feb 09, 2015 at 11:06:17PM -0500, Jason Baron wrote:
>> On 02/09/2015 04:50 PM, Peter Zijlstra wrote:
>>> On Mon, Feb 09, 2015 at 08:05:57PM +0000, Jason Baron wrote:
>>>> diff --git a/kernel/sched/wait.c b/kernel/sched/wait.c
>>>> index 852143a..17d1039 100644
>>>> --- a/kernel/sched/wait.c
>>>> +++ b/kernel/sched/wait.c
>>>> @@ -71,8 +71,11 @@ static void __wake_up_common(wait_queue_head_t *q, unsigned int mode,
>>>> unsigned flags = curr->flags;
>>>>
>>>> if (curr->func(curr, mode, wake_flags, key) &&
>>>> - (flags & WQ_FLAG_EXCLUSIVE) && !--nr_exclusive)
>>>> + (flags & WQ_FLAG_EXCLUSIVE) && !--nr_exclusive) {
>>>> + if (flags & WQ_FLAG_ROUND_ROBIN)
>>>> + list_move_tail(&curr->task_list, &q->task_list);
>>>> break;
>>>> + }
>>>> }
>>>> }
>>> I think you meant to write something like:
>>>
>>> if (curr->func(curr, mode, wake_flags, key) &&
>>> (flags & WQ_FLAG_EXCLUSIVE)) {
>>> if (flag & WQ_FLAG_ROUND_ROBIN)
>>> list_move_tail(&curr->task_list, &q->task_list);
>>> if (!--nr_exclusive)
>>> break;
>>> }
>>>
>>> Otherwise can only work for nr_exclusive==1.
>> Indeed. I'm also wondering if its worth avoiding the list_move_tail()
>> for the case where nr_exclusive is initially 0. IE the wake all case,
>> where we are just going to end up doing a bunch of list_move_tail()
>> calls, but end up in the same state.
> After writing this email, it occurred to me that you could probably do
> this with a custom wake function.
>
> Where autoremove_wake_function() does a list_del_init() you could do a
> rotate_wake_function() that does list_move_tail().
>
> That would avoid the entire WQ flag muckery.
hmmm...but don't we need the head/tail of the list to add it back too?
Further, we can't just append to tail while walking the list b/c
otherwise it can result in multiple wakeups to the same item. So I could
add to a local list, for example, in __wake_up_common(). And then just
add that to the tail once the list_for_each() finishes.
In terms of the flag, maybe another option would be to have the
wait_queue_func_t return a 'ROTATE_ME' value instead
of 1, since I think we currently only make use of 0 and 1?
Thanks,
-Jason
next prev parent reply other threads:[~2015-02-10 15:59 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-02-09 20:05 [PATCH 0/2] Add epoll round robin wakeup mode Jason Baron
2015-02-09 20:05 ` [PATCH 1/2] sched/wait: add " Jason Baron
2015-02-09 20:26 ` Michael Kerrisk
2015-02-09 21:50 ` Peter Zijlstra
2015-02-10 4:06 ` Jason Baron
2015-02-10 9:03 ` Peter Zijlstra
2015-02-10 15:59 ` Jason Baron [this message]
2015-02-10 16:11 ` Peter Zijlstra
2015-02-09 20:06 ` [PATCH 2/2] epoll: introduce EPOLLEXCLUSIVE and EPOLLROUNDROBIN Jason Baron
2015-02-09 20:18 ` Andy Lutomirski
2015-02-09 21:32 ` Jason Baron
2015-02-09 22:45 ` Andy Lutomirski
2015-02-10 3:59 ` Jason Baron
2015-02-10 4:49 ` Eric Wong
2015-02-10 19:16 ` Jason Baron
2015-02-10 19:32 ` Eric Wong
2015-02-09 20:27 ` Michael Kerrisk
2015-02-09 20:25 ` [PATCH 0/2] Add epoll round robin wakeup mode Michael Kerrisk
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