linux-kernel - Re: [RFC][PATCH 12/13] sched/deadline: Introduce deadline servers

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Date:   Fri, 6 Sep 2019 10:36:16 +0100
From:   Juri Lelli <juri.lelli@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Dietmar Eggemann <dietmar.eggemann@....com>, mingo@...nel.org,
        linux-kernel@...r.kernel.org, luca.abeni@...tannapisa.it,
        bristot@...hat.com, balsini@...roid.com, dvyukov@...gle.com,
        tglx@...utronix.de, vpillai@...italocean.com, rostedt@...dmis.org
Subject: Re: [RFC][PATCH 12/13] sched/deadline: Introduce deadline servers

Hi,

On 30/08/19 13:24, Peter Zijlstra wrote:
> On Thu, Aug 08, 2019 at 11:45:46AM +0200, Juri Lelli wrote:
> > I'd like to take this last sentence back, I was able to run a few boot +
> > hackbench + shutdown cycles with the following applied (guess too much
> > debug printks around before).
> 
> I've changed that slightly; the merged delta looks like:

It looks like I had to further apply what follows on top of your latest
wip-deadline branch (d3138279c7f3) to make kvm boot.

--->8---
 kernel/fork.c       | 2 ++
 kernel/sched/core.c | 3 +--
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/fork.c b/kernel/fork.c
index 2852d0e76ea3..4f404fe1d9ab 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1983,6 +1983,8 @@ static __latent_entropy struct task_struct *copy_process(
 	p->sequential_io_avg	= 0;
 #endif
 
+	p->server = NULL;
+
 	/* Perform scheduler related setup. Assign this task to a CPU. */
 	retval = sched_fork(clone_flags, p);
 	if (retval)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 1fd2a8c68daf..d72579b93a9f 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3917,8 +3917,7 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
 		 * This is the fast path; it cannot be a DL server pick;
 		 * therefore even if @p == @prev, ->server must be NULL.
 		 */
-		if (prev->server)
-			p->server = NULL;
+		p->server = NULL;
 
 		return p;
 	}