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Date: Wed, 18 Jun 2014 19:29:30 -0700 From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> To: Andi Kleen <ak@...ux.intel.com> Cc: Dave Hansen <dave.hansen@...el.com>, LKML <linux-kernel@...r.kernel.org>, Josh Triplett <josh@...htriplett.org>, "Chen, Tim C" <tim.c.chen@...el.com>, Christoph Lameter <cl@...ux.com> Subject: Re: [bisected] pre-3.16 regression on open() scalability On Wed, Jun 18, 2014 at 07:13:37PM -0700, Paul E. McKenney wrote: > On Wed, Jun 18, 2014 at 06:42:00PM -0700, Andi Kleen wrote: > > > > I still think it's totally the wrong direction to pollute so > > many fast paths with this obscure debugging check workaround > > unconditionally. > > OOM prevention should count for something, I would hope. > > > cond_resched() is in EVERY sleeping lock and in EVERY memory allocation! > > And these are really critical paths for many workloads. > > > > If you really wanted to do this I think you would first need > > to define a cond_resched_i_am_not_fast() or somesuch. > > > > Or put it all behind some debugging ifdef. > > My first thought was to put it behind CONFIG_NO_HZ_FULL, but everyone > seems to be enabling that one. > > As mentioned earlier, I could potentially push the check behind > the need-resched check, which would get it off of the common case > of the code paths you call out above. Of course, it would also be good to measure this and see how much it really hurts. Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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