Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754969Ab3H3JtF (ORCPT ); Fri, 30 Aug 2013 05:49:05 -0400 Received: from mail-ee0-f53.google.com ([74.125.83.53]:65017 "EHLO mail-ee0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754336Ab3H3JtD (ORCPT ); Fri, 30 Aug 2013 05:49:03 -0400 Date: Fri, 30 Aug 2013 11:48:58 +0200 From: Ingo Molnar To: Sedat Dilek Cc: Linus Torvalds , Waiman Long , Benjamin Herrenschmidt , Alexander Viro , Jeff Layton , Miklos Szeredi , Ingo Molnar , Thomas Gleixner , linux-fsdevel , Linux Kernel Mailing List , Peter Zijlstra , Steven Rostedt , Andi Kleen , "Chandramouleeswaran, Aswin" , "Norton, Scott J" Subject: Re: [PATCH v7 1/4] spinlock: A new lockref structure for lockless update of refcount Message-ID: <20130830094857.GA14502@gmail.com> References: <1377751465.4028.20.camel@pasglop> <20130829070012.GC27322@gmail.com> <52200DAE.2020303@hp.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3451 Lines: 85 * Sedat Dilek wrote: > On Fri, Aug 30, 2013 at 9:55 AM, Sedat Dilek wrote: > > On Fri, Aug 30, 2013 at 5:54 AM, Linus Torvalds > > wrote: > >> On Thu, Aug 29, 2013 at 8:12 PM, Waiman Long wrote: > >>> On 08/29/2013 07:42 PM, Linus Torvalds wrote: > >>>> > >>>> Waiman? Mind looking at this and testing? Linus > >>> > >>> Sure, I will try out the patch tomorrow morning and see how it works out for > >>> my test case. > >> > >> Ok, thanks, please use this slightly updated patch attached here. > >> > >> It improves on the previous version in actually handling the > >> "unlazy_walk()" case with native lockref handling, which means that > >> one other not entirely odd case (symlink traversal) avoids the d_lock > >> contention. > >> > >> It also refactored the __d_rcu_to_refcount() to be more readable, and > >> adds a big comment about what the heck is going on. The old code was > >> clever, but I suspect not very many people could possibly understand > >> what it actually did. Plus it used nested spinlocks because it wanted > >> to avoid checking the sequence count twice. Which is stupid, since > >> nesting locks is how you get really bad contention, and the sequence > >> count check is really cheap anyway. Plus the nesting *really* didn't > >> work with the whole lockref model. > >> > >> With this, my stupid thread-lookup thing doesn't show any spinlock > >> contention even for the "look up symlink" case. > >> > >> It also avoids the unnecessary aligned u64 for when we don't actually > >> use cmpxchg at all. > >> > >> It's still one single patch, since I was working on lots of small > >> cleanups. I think it's pretty close to done now (assuming your testing > >> shows it performs fine - the powerpc numbers are promising, though), > >> so I'll split it up into proper chunks rather than random commit > >> points. But I'm done for today at least. > >> > >> NOTE NOTE NOTE! My test coverage really has been pretty pitiful. You > >> may hit cases I didn't test. I think it should be *stable*, but maybe > >> there's some other d_lock case that your tuned waiting hid, and that > >> my "fastpath only for unlocked case" version ends up having problems > >> with. > >> > > > > Following this thread with half an eye... Was that "unsigned" stuff > > fixed (someone pointed to it). > > How do you call that test-patch (subject)? > > I would like to test it on my SNB ultrabook with your test-case script. > > > > Here on Ubuntu/precise v12.04.3 AMD64 I get these numbers for total loops: > > lockref: w/o patch | w/ patch > ====================== > Run #1: 2.688.094 | 2.643.004 > Run #2: 2.678.884 | 2.652.787 > Run #3: 2.686.450 | 2.650.142 > Run #4: 2.688.435 | 2.648.409 > Run #5: 2.693.770 | 2.651.514 > > Average: 2687126,6 VS. 2649171,2 ( ???37955,4 ) For precise stddev numbers you can run it like this: perf stat --null --repeat 5 ./test and it will measure time only and print the stddev in percentage: Performance counter stats for './test' (5 runs): 1.001008928 seconds time elapsed ( +- 0.00% ) Thanks, Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/