linux-kernel - Re: sched: tweak select_idle_sibling to look for idle threads

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Message-ID: <20160506071251.GM3448@twins.programming.kicks-ass.net>
Date:	Fri, 6 May 2016 09:12:51 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Chris Mason <clm@...com>, Mike Galbraith <mgalbraith@...e.de>,
	Ingo Molnar <mingo@...nel.org>,
	Matt Fleming <matt@...eblueprint.co.uk>,
	linux-kernel@...r.kernel.org
Subject: Re: sched: tweak select_idle_sibling to look for idle threads

On Thu, May 05, 2016 at 09:58:44AM -0400, Chris Mason wrote:
> > I'll try and have a prod at the program itself if you have no pending
> > changes on your end.
> 
> Sorry, I don't.  Look at sleep_for_runtime() and how I test/set the
> global stopping variable in different places.  I've almost certainly got
> someone waiting on a wakeup that'll never come.

The below makes it go..

---
 schbench.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/schbench.c b/schbench.c
index a0e9f7e..f299959 100644
--- a/schbench.c
+++ b/schbench.c
@@ -49,7 +49,7 @@ static int pipe_test = 0;
 static unsigned int max_us = 50000;
 
 /* the message threads flip this to true when they decide runtime is up */
-static unsigned long stopping = 0;
+static volatile unsigned long stopping = 0;
 
 
 /*
@@ -746,8 +746,8 @@ static void sleep_for_runtime()
 		else
 			break;
 	}
-	stopping = 1;
 	__sync_synchronize();
+	stopping = 1;
 }
 
 int main(int ac, char **av)