On 3 September 2014 14:26, Preeti U Murthy preeti@linux.vnet.ibm.com wrote:
On 09/03/2014 05:14 PM, Vincent Guittot wrote:
On 3 September 2014 11:11, Preeti U Murthy preeti@linux.vnet.ibm.com wrote:
On 09/01/2014 02:15 PM, Vincent Guittot wrote:
[snip]
Ok I understand your explanation above. But I was wondering if you would need to add this check around rq->cfs.h_nr_running >= 1 in the above two cases as well.
yes you're right for the test if (rq->nr_running >= 2).
It's not so straight forward for nr_busy_cpus which reflects how many CPUs have not stopped their tick. The scheduler assumes that the latter are busy with cfs tasks
I have actually raised this concern over whether we should be using rq->nr_running or cfs_rq->nr_running while we do load balancing in reply to your patch3. While all our load measurements are about the cfs_rq
I have just replied to your comments on patch 3. Sorry for the delay
load, we use rq->nr_running, which may include tasks from other sched classes as well. We divide them to get average load per task during load balancing which is wrong, isn't it? Similarly during nohz_kick_needed(), we trigger load balancing based on rq->nr_running again.
In this patch too, even if you know that the cpu is being dominated by tasks that do not belong to cfs class, you would be triggering a futile load balance if there are no fair tasks to move.
This patch adds one additional condition that is based on rq->cfs.h_nr_running so it should not trigger any futile load balance. Then, I have also take advantage of this patch to clean up nohz_kick_needed as proposed by Peter but the conditions are the same than previously (except the one with rq->cfs.h_nr_running)
I can prepare another patchset that will solve the concerns that you raised for nohz_kick_needed and in patch 3 but i would prefer not include them in this patchset which is large enough and which subject is a bit different. Does it seem ok for you ?
Sure Vincent, thanks! I have in fact sent out a mail raising my concern over rq->nr_running. If others agree on the issue to be existing, maybe we can work on this next patchset that can clean this up in all places necessary and not just in nohz_kick_needed().
Ok, let continue this discussion on the other thread
Regards, Vincent
Regards Preeti U Murthy
Regards, Vincent
Regards Preeti U Murthy