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

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Message-ID: <20140618001517.GL8178@tassilo.jf.intel.com>
Date:	Tue, 17 Jun 2014 17:15:17 -0700
From:	Andi Kleen <ak@...ux.intel.com>
To:	Dave Hansen <dave.hansen@...el.com>
Cc:	paulmck@...ux.vnet.ibm.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

> It also ends up eating a new cacheline in a bunch of pretty hot paths.
> It would be nice to be able to keep the fast path part of this as at
> least read-only.
> 
> Could we do something (functionally) like the attached patch?  Instead
> of counting cond_resched() calls, we could just specify some future time
> by which we want have a quiescent state.  We could even push the time to
> be something _just_ before we would have declared a stall.

I still think it's totally the wrong place. cond_resched() is in so
many fast paths (every lock, every allocation). It just doesn't
make sense to add non essential things like this to it.

I would be rather to just revert the original patch.

-Andi
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