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

From: Peter Zijlstra <peterz@infradead.org>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Dave Hansen <dave@sr71.net>, Andi Kleen <ak@linux.intel.com>,
	dave.hansen@linux.intel.com, akpm@linux-foundation.org,
	jack@suse.cz, viro@zeniv.linux.org.uk, eparis@redhat.com,
	john@johnmccutchan.com, rlove@rlove.org,
	tim.c.chen@linux.intel.com, linux-kernel@vger.kernel.org
Subject: Re: [RFC][PATCH] fs: optimize inotify/fsnotify code for unwatched files
Date: Mon, 22 Jun 2015 17:20:13 +0200	[thread overview]
Message-ID: <20150622152013.GW3644@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20150622151121.GK3913@linux.vnet.ibm.com>

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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