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authorNadav Har'El <nyh@math.technion.ac.il>2012-02-27 15:07:29 +0200
committerMichael S. Tsirkin <mst@redhat.com>2012-02-28 09:13:19 +0200
commitd550dda192c1bd039afb774b99485e88b70d7cb8 (patch)
tree1376f2daf6be6d170a57e8e9b27411cf2fab6191 /drivers/vhost
parentb17d5c6e190f3d328aae0444f8b93d58d0015714 (diff)
downloadlinux-linaro-stable-d550dda192c1bd039afb774b99485e88b70d7cb8.tar.gz
vhost: don't forget to schedule()
This is a tiny, but important, patch to vhost. Vhost's worker thread only called schedule() when it had no work to do, and it wanted to go to sleep. But if there's always work to do, e.g., the guest is running a network-intensive program like netperf with small message sizes, schedule() was *never* called. This had several negative implications (on non-preemptive kernels): 1. Passing time was not properly accounted to the "vhost" process (ps and top would wrongly show it using zero CPU time). 2. Sometimes error messages about RCU timeouts would be printed, if the core running the vhost thread didn't schedule() for a very long time. 3. Worst of all, a vhost thread would "hog" the core. If several vhost threads need to share the same core, typically one would get most of the CPU time (and its associated guest most of the performance), while the others hardly get any work done. The trivial solution is to add if (need_resched()) schedule(); After doing every piece of work. This will not do the heavy schedule() all the time, just when the timer interrupt decided a reschedule is warranted (so need_resched returns true). Thanks to Abel Gordon for this patch. Signed-off-by: Nadav Har'El <nyh@il.ibm.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Diffstat (limited to 'drivers/vhost')
-rw-r--r--drivers/vhost/vhost.c2
1 files changed, 2 insertions, 0 deletions
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index c14c42b95ab8..ae66278e4dcf 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -222,6 +222,8 @@ static int vhost_worker(void *data)
if (work) {
__set_current_state(TASK_RUNNING);
work->fn(work);
+ if (need_resched())
+ schedule();
} else
schedule();