RE: [patch] sched: improve pinned task handling again!

["Chen, Kenneth W" <kenneth.w.chen@intel.com>]

Siddha, Suresh B wrote on Friday, April 01, 2005 8:05 PM
> On Sat, Apr 02, 2005 at 01:11:20PM +1000, Nick Piggin wrote:
> > 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.
>
> Ken initially observed with older kernels(2.4 kernel with Ingo's sched),
> it was happening with few hundred processes. 2.6 is not that bad and it
> improved with recent fixes. It is not very important. We want to raise
> the flag and see if we can comeup with a decent solution.

The livelock is observed with an in-house stress test suite.  The original
intent of that test is remotely connected to stress the kernel.  It is by
accident that it triggered a kernel issue.  Though, we are now worried that
this can be used as a DOS attack.


Nick Piggin wrote on Friday, April 01, 2005 7:11 PM
> > 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?

This sounds plausible, though my first try did not yield desired result
(i.e., still hangs the kernel, I might missed a few things here and there).