Re: [bisected] pre-3.16 regression on open() scalability

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

On Thu, Jun 19, 2014 at 02:32:03PM -0700, josh@joshtriplett.org wrote:
> On Thu, Jun 19, 2014 at 04:16:34PM -0500, Christoph Lameter wrote:
> > This looks very much like the CONFIG_PREEMPT problem in not so
> > extreme form. Maybe we need to add another config option:
> > 
> > CONFIG_REALLY_REALLY_NO_PREEMPT
> > 
> > to get the fastest code possible and those cond_rescheds removed from the
> > critical paths?
> > 
> > Or better
> > 
> > CONFIG_PREEMPT_HALF_WAY
> > 
> > to enable those cond_rescheds.
> 
> That much actually does seem quite reasonable: making cond_resched() do
> non-trivial work ought to have a config option to disable it.

I am putting together patches based on Eric Dumazet's suggestion and on a
variant of the above approach.  However, I do expect the distros to starve
to death between those two bales of hay.  But perhaps the actual patches
will inspire a bit of light to go with this thread's heat and smoke.

							Thanx, Paul