Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754694Ab3I1Tdk (ORCPT ); Sat, 28 Sep 2013 15:33:40 -0400 Received: from mail-vb0-f53.google.com ([209.85.212.53]:52531 "EHLO mail-vb0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751248Ab3I1Tdh (ORCPT ); Sat, 28 Sep 2013 15:33:37 -0400 MIME-Version: 1.0 In-Reply-To: <20130928192123.GA8228@gmail.com> References: <1380308424-31011-1-git-send-email-Waiman.Long@hp.com> <20130928074144.GA17773@gmail.com> <20130928192123.GA8228@gmail.com> Date: Sat, 28 Sep 2013 12:33:36 -0700 X-Google-Sender-Auth: zNzeNe836bDFImxtWTusDL8Edns Message-ID: Subject: Re: [PATCH] rwsem: reduce spinlock contention in wakeup code path From: Linus Torvalds To: Ingo Molnar Cc: Waiman Long , Ingo Molnar , Andrew Morton , Linux Kernel Mailing List , Rik van Riel , Peter Hurley , Davidlohr Bueso , Alex Shi , Tim Chen , Peter Zijlstra , Andrea Arcangeli , Matthew R Wilcox , Dave Hansen , Michel Lespinasse , Andi Kleen , "Chandramouleeswaran, Aswin" , "Norton, Scott J" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1560 Lines: 34 On Sat, Sep 28, 2013 at 12:21 PM, Ingo Molnar wrote: > > If we do that then I suspect the next step will be queued rwlocks :-/ The > current rwlock_t implementation is rather primitive by modern standards. > (We'd probably have killed rwlock_t long ago if not for the > tasklist_lock.) Yeah, I'm not happy about or rwlocks. That's one lock that currently is so broken that I think we could easily argue for making that one queued. Waiman had a qrwlock series that looked reasonable, and I think his later versions were drop-in replacements (ie they automatically just did the RightThing(tm) wrt interrupts taking a recursive read lock - I objected to the first versions that required that to be stated explicitly). I think Waiman's patches (even the later ones) made the queued rwlocks be a side-by-side implementation with the old rwlocks, and I think that was just being unnecessarily careful. It might be useful for testing to have a config option to switch between the two, but we might as well go all the way. The old rwlock's really have been a disappointment - they are slower than spinlocks, and seldom/never end up scaling any better. Their main advantage was literally the irq behavior - allowing readers to happen without the expense of worrying about irq's. Linus -- 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/