On 02/27/2012 03:07 PM, Nadav Har'El wrote:
> 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@xxxxxxxxxx>
> ---
> vhost.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index c14c42b..ae66278 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();
>
This is cond_resched(), no?
--
error compiling committee.c: too many arguments to function
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