linux-kernel - Re: [RFC][PATCH] fs: optimize inotify/fsnotify code for unwatched files

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Message-ID: <20150622152013.GW3644@twins.programming.kicks-ass.net>
Date:	Mon, 22 Jun 2015 17:20:13 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Dave Hansen <dave@...1.net>, Andi Kleen <ak@...ux.intel.com>,
	dave.hansen@...ux.intel.com, akpm@...ux-foundation.org,
	jack@...e.cz, viro@...iv.linux.org.uk, eparis@...hat.com,
	john@...nmccutchan.com, rlove@...ve.org,
	tim.c.chen@...ux.intel.com, linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH] fs: optimize inotify/fsnotify code for unwatched
 files

On Mon, Jun 22, 2015 at 08:11:21AM -0700, Paul E. McKenney wrote:
> That depends on how slow the resulting slow global state would be.
> We have some use cases (definitely KVM, perhaps also some of the VFS
> code) that need the current speed, as opposed to the profound slowness
> that three trips through synchronize_sched() would provide. 

But we have call_srcu() these days, not everything needs to use
sync_srcu() anymore. Although I've not checked recently.

> Plus we
> would lose the ability to have SRCU readers on idle and offline CPUs.

Are we actually doing that? offline CPUs in particular seems iffy, I
don't think we need (or should) worry about that. I know its been an
issue with regular RCU due to tracing, but I'm not sure we should care
for it for SRCU.
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