linux-kernel - [PATCH] steal_account_process

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Message-ID: <56DA1339.5030601@mail.usask.ca>
Date:	Fri, 04 Mar 2016 16:59:05 -0600
From:	Chris Friesen <cbf123@...l.usask.ca>
To:	John Stultz <john.stultz@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	lkml <linux-kernel@...r.kernel.org>
Subject: [PATCH] steal_account_process_tick() should return jiffies

The callers of steal_account_process_tick() expect it to return whether
the last jiffy was stolen or not.

Currently the return value of steal_account_process_tick() is in units
of cputime, which vary between either jiffies or nsecs depending on
CONFIG_VIRT_CPU_ACCOUNTING_GEN.

The fix is to change steal_account_process_tick() to always return
jiffies.  If CONFIG_VIRT_CPU_ACCOUNTING_GEN is not enabled then this
is a no-op.

As far as I can tell this bug has been present since commit dee08a72.

Signed-off-by: Chris Friesen <chris.friesen@...driver.com>
---

 kernel/sched/cputime.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index b2ab2ff..e724496 100644
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -276,7 +276,7 @@ static __always_inline bool steal_account_process_tick(void)
 		this_rq()->prev_steal_time += cputime_to_nsecs(steal_ct);

 		account_steal_time(steal_ct);
-		return steal_ct;
+		return cputime_to_jiffies(steal_ct);
 	}
 #endif
 	return false;