Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754406Ab3H3J1G (ORCPT ); Fri, 30 Aug 2013 05:27:06 -0400 Received: from mail-wi0-f182.google.com ([209.85.212.182]:53544 "EHLO mail-wi0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752766Ab3H3J1E convert rfc822-to-8bit (ORCPT ); Fri, 30 Aug 2013 05:27:04 -0400 MIME-Version: 1.0 Reply-To: sedat.dilek@gmail.com In-Reply-To: References: <1375758759-29629-1-git-send-email-Waiman.Long@hp.com> <1375758759-29629-2-git-send-email-Waiman.Long@hp.com> <1377751465.4028.20.camel@pasglop> <20130829070012.GC27322@gmail.com> <52200DAE.2020303@hp.com> Date: Fri, 30 Aug 2013 11:27:01 +0200 Message-ID: Subject: Re: [PATCH v7 1/4] spinlock: A new lockref structure for lockless update of refcount From: Sedat Dilek To: Linus Torvalds Cc: Waiman Long , Ingo Molnar , 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" Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2966 Lines: 70 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 ) - Sedat - -- 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/