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Message-ID: <4f571c5c759b9d356d1bb4114fb169181194a780.camel@gmx.de>
Subject: Re: wakeup_affine_weight() is b0rked - was Re: [PATCH 2/2]
 sched/fair: Scale wakeup granularity relative to nr_running
From:   Mike Galbraith <efault@gmx.de>
To:     Barry Song <21cnbao@gmail.com>
Cc:     Mel Gorman <mgorman@techsingularity.net>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@kernel.org>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Valentin Schneider <valentin.schneider@arm.com>,
        Aubrey Li <aubrey.li@linux.intel.com>,
        Barry Song <song.bao.hua@hisilicon.com>,
        Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
        LKML <linux-kernel@vger.kernel.org>
Date:   Mon, 04 Oct 2021 11:06:30 +0200
In-Reply-To: <f1b421f956fa044b4efa7f5fef015725b27223cf.camel@gmx.de>
References: <20210920142614.4891-1-mgorman@techsingularity.net>
         <20210920142614.4891-3-mgorman@techsingularity.net>
         <22e7133d674b82853a5ee64d3f5fc6b35a8e18d6.camel@gmx.de>
         <20210921103621.GM3959@techsingularity.net>
         <ea2f9038f00d3b4c0008235079e1868145b47621.camel@gmx.de>
         <02c977d239c312de5e15c77803118dcf1e11f216.camel@gmx.de>
         <CAGsJ_4xcRFcDMpuC7vrpHe=aRbDpAnRd1F64aqh2EEcNgmZxCg@mail.gmail.com>
         <f1b421f956fa044b4efa7f5fef015725b27223cf.camel@gmx.de>
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On Mon, 2021-10-04 at 06:34 +0200, Mike Galbraith wrote:
> On Sun, 2021-10-03 at 20:34 +1300, Barry Song wrote:
> >
> > I am wondering if this should be the responsibility of wake_wide()?
>
> Those event threads we stacked so high (which are kde minions btw),
> don't generally accrue _any_ wakee_flips, so when X wakes a slew of the
> things, wake_wide()'s heuristic rejects the lot.
>
> So yeah, the blame game for this issue is a target rich environment.
> Shoot either of 'em (or both), and you'll hit the bad guy.

The mallet below convinced wake_wide() that X waking event threads is
something it most definitely should care about.  It's not perfect, can
get caught with its pants down, because behavior changes a LOT, but I
at least have to work at it a bit to stack tasks to the ceiling.

With make -j8 running along with firefox with two tabs, one containing
youtube's suggestions of stuff you probably don't want to watch, the
other a running clip, if I have the idle tab in focus, and don't drive
mouse around, flips decay enough for wake_wide() to lose interest, but
just wiggle the mouse, and it starts waking wide. Focus on the running
clip, and it continuously wakes wide. =C2=A0

Hacky, but way better behavior.. at this particular testcase.. in this
particular box.. at least once :)

=2D--
 kernel/sched/fair.c |   10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

=2D-- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5865,6 +5865,14 @@ static void record_wakee(struct task_str
 	}

 	if (current->last_wakee !=3D p) {
+		int min =3D __this_cpu_read(sd_llc_size) << 1;
+		/*
+		 * Couple the wakee flips to the waker for the case where it
+		 * doesn't accrue flips, taking care to not push the wakee
+		 * high enough that the wake_wide() heuristic fails.
+		 */
+		if (current->wakee_flips > p->wakee_flips * min)
+			p->wakee_flips++;
 		current->last_wakee =3D p;
 		current->wakee_flips++;
 	}
@@ -5895,7 +5903,7 @@ static int wake_wide(struct task_struct

 	if (master < slave)
 		swap(master, slave);
-	if (slave < factor || master < slave * factor)
+	if ((slave < factor && master < (factor>>1)*factor) || master < slave * =
factor)
 		return 0;
 	return 1;
 }