lkml.org 
[lkml]   [2008]   [Oct]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Subject[PATCH] sched_clock: prevent scd->clock from moving backwards
From
Date
sched_clock: prevent scd->clock from moving backwards

When sched_clock_cpu() couples the clocks between two cpus, it may
increment scd->clock beyond the GTOD tick window that __update_sched_clock()
uses to clamp the clock. A later call to __update_sched_clock() may move
the clock back to scd->tick_gtod + TICK_NSEC, violating the clock's
monotonic property.

This patch ensures that scd->clock will not be set backward.

Signed-off-by: Dave Kleikamp <shaggy@linux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>

diff --git a/kernel/sched_clock.c b/kernel/sched_clock.c
index e8ab096..a989d64 100644
--- a/kernel/sched_clock.c
+++ b/kernel/sched_clock.c
@@ -118,13 +118,13 @@ static u64 __update_sched_clock(struct sched_clock_data *scd, u64 now)

/*
* scd->clock = clamp(scd->tick_gtod + delta,
- * max(scd->tick_gtod, scd->clock),
- * scd->tick_gtod + TICK_NSEC);
+ * max(scd->tick_gtod, scd->clock),
+ * min(scd->clock, scd->tick_gtod + TICK_NSEC));
*/

clock = scd->tick_gtod + delta;
min_clock = wrap_max(scd->tick_gtod, scd->clock);
- max_clock = scd->tick_gtod + TICK_NSEC;
+ max_clock = wrap_min(scd->clock, scd->tick_gtod + TICK_NSEC);

clock = wrap_max(clock, min_clock);
clock = wrap_min(clock, max_clock);



\
 
 \ /
  Last update: 2008-10-08 15:05    [W:0.051 / U:2.576 seconds]
©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site