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From: Yuyang Du <yuyang.du@intel.com>
To: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	mingo@kernel.org, linux-kernel@vger.kernel.org,
	bsegall@google.com, pjt@google.com, morten.rasmussen@arm.com,
	vincent.guittot@linaro.org, dietmar.eggemann@arm.com
Subject: Re: [RFC PATCH 1/2] sched: Clean up SD_BALANCE_WAKE flags in sched domain build-up
Date: Wed, 1 Jun 2016 08:01:05 +0800	[thread overview]
Message-ID: <20160601000105.GU18670@intel.com> (raw)
In-Reply-To: <1464757633.4023.39.camel@gmail.com>

On Wed, Jun 01, 2016 at 07:07:13AM +0200, Mike Galbraith wrote:
> On Tue, 2016-05-31 at 09:31 +0800, Yuyang Du wrote:
> > On Tue, May 31, 2016 at 11:21:46AM +0200, Peter Zijlstra wrote:
> > > On Tue, May 31, 2016 at 09:11:37AM +0800, Yuyang Du wrote:
> > > > The SD_BALANCE_WAKE is irrelevant in the contexts of these two removals,
> > > > and in addition SD_BALANCE_WAKE is not and should not be set in any
> > > > sched_domain flags so far.
> > > 
> > > This Changelog doesn't make any sense...
> > 
> > How? SD_BALANCE_WAKE is not in any sched_domain flags (sd->flags), even if
> > it is, it is not used anywhere, no?
> 
> If the user chooses to set SD_BALANCE_WAKE in sd->flags, it is in fact
> used.  It's just not turned on by default due to full balance on every
> wakeup being far too painful to do by default.

Yup. Up to this point, we don't have any disagreement. And I don't think we
have any disagreement conceptually. What the next patch really does is:

(1) we don't remove SD_BALANCE_WAKE as an important sched_domain flag, on
    the contrary, we strengthen it.

(2) the semantic of SD_BALANCE_WAKE is currently represented by SD_WAKE_AFFINE,
    we actually remove this representation.

(3) regarding the semantic of SD_WAKE_AFFINE, it is really not about selecting
    waker CPU or about the fast path. Conceptually, it is just saying the waker
    CPU is a valid and important candidate if SD_BALANCE_WAKE, which is just so
    obvious, so I don't think it deserves to be a separate sched_domain flag.

(4) the outcome is, if SD_BALANCE_WAKE, we definitely will/should try waker CPU,
    and if !SD_BALANCE_WAKE, we don't try waker CPU. So nothing functional is
    changed.

  reply	other threads:[~2016-06-01  7:58 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-05-31  1:11 [RFC PATCH 0/2] Remove and replace SD_WAKE_AFFINE with SD_BALANCE_WAKE Yuyang Du
2016-05-31  1:11 ` [RFC PATCH 1/2] sched: Clean up SD_BALANCE_WAKE flags in sched domain build-up Yuyang Du
2016-05-31  9:21   ` Peter Zijlstra
2016-05-31  1:31     ` Yuyang Du
2016-05-31 10:41       ` Peter Zijlstra
2016-05-31 18:00         ` Yuyang Du
2016-06-01  5:07       ` Mike Galbraith
2016-06-01  0:01         ` Yuyang Du [this message]
2016-06-01  8:32           ` Vincent Guittot
2016-06-01  1:03             ` Yuyang Du
2016-06-01  9:24               ` Vincent Guittot
2016-06-01 19:35                 ` Yuyang Du
2016-06-02  6:56                   ` Vincent Guittot
2016-06-01 23:19                     ` Yuyang Du
2016-06-01  9:36           ` Mike Galbraith
2016-06-01 20:03             ` Yuyang Du
2016-06-02  5:50               ` Mike Galbraith
2016-06-01 22:41                 ` Yuyang Du
2016-06-02  6:44                   ` Mike Galbraith
2016-05-31  1:11 ` [RFC PATCH 2/2] sched: Remove SD_WAKE_AFFINE flag and replace it with SD_BALANCE_WAKE Yuyang Du
2016-05-31  9:23   ` Peter Zijlstra
2016-05-31  1:34     ` Yuyang Du

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