linux-kernel - Re: [PATCH v7 1/4] spinlock: A new lockref structure for lockless update of refcount

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Date:	Fri, 30 Aug 2013 12:33:49 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Waiman Long <waiman.long@...com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Jeff Layton <jlayton@...hat.com>,
	Miklos Szeredi <mszeredi@...e.cz>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Andi Kleen <andi@...stfloor.org>,
	"Chandramouleeswaran, Aswin" <aswin@...com>,
	"Norton, Scott J" <scott.norton@...com>
Subject: Re: [PATCH v7 1/4] spinlock: A new lockref structure for lockless
 update of refcount

On Fri, Aug 30, 2013 at 12:20 PM, Waiman Long <waiman.long@...com> wrote:
>
> Below is the perf data of my short workloads run in an 80-core DL980:

Ok, that doesn't look much like d_lock any more. Sure, there's a small
amount of spinlocking going on with lockref being involved, but on the
whole even that looks more like getcwd and other random things.

I do agree that getcwd() can probably be hugely optimized. Nobody has
ever bothered, because it's never really performance-critical, and I
think AIM7 ends up just doing something really odd. I bet we could fix
it entirely if we cared enough.

I just wonder if it's even worth it (I assume AIM7 is something HP
uses internally, because I've never really heard of anybody else
caring)

But I'll look at getcwd anyway.

                Linus
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