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Message-ID: <20160714163731.GF30154@twins.programming.kicks-ass.net>
Date: Thu, 14 Jul 2016 18:37:31 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Oleg Nesterov <oleg@...hat.com>
Cc: Tejun Heo <tj@...nel.org>, John Stultz <john.stultz@...aro.org>,
Ingo Molnar <mingo@...hat.com>,
lkml <linux-kernel@...r.kernel.org>,
Dmitry Shmidt <dimitrysh@...gle.com>,
Rom Lemarchand <romlem@...gle.com>,
Colin Cross <ccross@...gle.com>, Todd Kjos <tkjos@...gle.com>,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: Severe performance regression w/ 4.4+ on Android due to cgroup
locking changes
On Thu, Jul 14, 2016 at 04:58:44PM +0200, Oleg Nesterov wrote:
>
> But note that we do not need RCU_NONE. All we need is the trivial change
> below.
Hurm, maybe. So having that unbalanced keeps us in GP_PASSED state and
since we'll never drop gp_count back to 0 nothing will ever happen.
Cute, yes.
> Damn, I am trying to find my old rcu-sync patches which I didn't
> send, but can't... OK, this almost off-topic right now, just this "enter"
> is ugly and we can't switch the slow/fast modes dynamically.
>
> The rest of you patch is "optimize the slow path" and we already discussed
> it before, I personally like it. Perhaps you can redo it without RCU_NONE
> part?
Indeed, I rebased that patch on top of the current tree and had to add
support for down_trylock() but otherwise much the same thing.
I can send it out again.
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