From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932626AbbBIU0Z (ORCPT ); Mon, 9 Feb 2015 15:26:25 -0500 Received: from mail-ob0-f173.google.com ([209.85.214.173]:40643 "EHLO mail-ob0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760201AbbBIU0W (ORCPT ); Mon, 9 Feb 2015 15:26:22 -0500 MIME-Version: 1.0 In-Reply-To: References: From: Michael Kerrisk Date: Mon, 9 Feb 2015 21:26:01 +0100 X-Google-Sender-Auth: f6or7UYJWaYSKQgaCtbBLSU9IGM Message-ID: Subject: Re: [PATCH 1/2] sched/wait: add round robin wakeup mode To: Jason Baron Cc: Peter Zijlstra , Ingo Molnar , Al Viro , Andrew Morton , normalperson@yhbt.net, Davide Libenzi , Linux Kernel , Linux-Fsdevel , Linux API Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org [CC += linux-api@vger.kernel.org] On Mon, Feb 9, 2015 at 9:05 PM, Jason Baron wrote: > The motivation for this flag is to allow the distribution of wakeups from > a shared source in a balanced manner. Currently, we can add threads exclusively > but that often results in the same thread woken up again and again. In the case > where we are trying to balance work across threads this is not desirable. > > The WQ_FLAG_ROUND_ROBIN is restricted to being exclusive as well, otherwise we > do not know who is being woken up. > > Signed-off-by: Jason Baron > --- > include/linux/wait.h | 11 +++++++++++ > kernel/sched/wait.c | 5 ++++- > 2 files changed, 15 insertions(+), 1 deletion(-) > > diff --git a/include/linux/wait.h b/include/linux/wait.h > index 2232ed1..bbdef98 100644 > --- a/include/linux/wait.h > +++ b/include/linux/wait.h > @@ -16,6 +16,7 @@ int default_wake_function(wait_queue_t *wait, unsigned mode, int flags, void *ke > /* __wait_queue::flags */ > #define WQ_FLAG_EXCLUSIVE 0x01 > #define WQ_FLAG_WOKEN 0x02 > +#define WQ_FLAG_ROUND_ROBIN 0x04 > > struct __wait_queue { > unsigned int flags; > @@ -109,6 +110,16 @@ static inline int waitqueue_active(wait_queue_head_t *q) > > extern void add_wait_queue(wait_queue_head_t *q, wait_queue_t *wait); > extern void add_wait_queue_exclusive(wait_queue_head_t *q, wait_queue_t *wait); > + > +/* > + * rr relies on exclusive, otherwise we don't know which entry was woken > + */ > +static inline void add_wait_queue_rr(wait_queue_head_t *q, wait_queue_t *wait) > +{ > + wait->flags |= WQ_FLAG_ROUND_ROBIN; > + add_wait_queue_exclusive(q, wait); > +} > + > extern void remove_wait_queue(wait_queue_head_t *q, wait_queue_t *wait); > > static inline void __add_wait_queue(wait_queue_head_t *head, wait_queue_t *new) > 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; > + } > } > } > > -- > 1.8.2.rc2 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Author of "The Linux Programming Interface", http://blog.man7.org/