Messages in this thread | | | Date | Sat, 02 Apr 2005 13:11:20 +1000 | From | Nick Piggin <> | Subject | Re: [patch] sched: improve pinned task handling again! |
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Siddha, Suresh B wrote:
> > This time Ken Chen brought up this issue -- No it has nothing to do with > industry db benchmark ;-) > > Even with the above mentioned Nick's patch in -mm, I see system livelock's > if for example I have 7000 processes pinned onto one cpu (this is on the > fastest 8-way system I have access to). I am sure there will be other > systems where this problem can be encountered even with lesser pin count. >
Thanks for testing these patches in -mm, by the way.
> We tried to fix this issue but as you know there is no good mechanism > in fixing this issue with out letting the regular paths know about this. > > Our proposed solution is appended and we tried to minimize the affect on > fast path. It builds up on Nick's patch and once this situation is detected, > it will not do any more move_tasks as long as busiest cpu is always the > same cpu and the queued processes on busiest_cpu, their > cpu affinity remain same(found out by runqueue's "generation_num") >
7000 running processes pinned into one CPU. I guess that isn't a great deal :(
How important is this? Any application to real workloads? Even if not, I agree it would be nice to improve this more. I don't know if I really like this approach - I guess due to what it adds to fastpaths.
Now presumably if the all_pinned logic is working properly in the first place, and it is correctly causing balancing to back-off, you could tweak that a bit to avoid livelocks? Perhaps the all_pinned case should back off faster than the usual doubling of the interval, and be allowed to exceed max_interval?
Any thoughts Ingo?
-- SUSE Labs, Novell Inc.
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