Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261454AbVA1QRN (ORCPT ); Fri, 28 Jan 2005 11:17:13 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261455AbVA1QRN (ORCPT ); Fri, 28 Jan 2005 11:17:13 -0500 Received: from mx2.elte.hu ([157.181.151.9]:39811 "EHLO mx2.elte.hu") by vger.kernel.org with ESMTP id S261454AbVA1QRJ (ORCPT ); Fri, 28 Jan 2005 11:17:09 -0500 Date: Fri, 28 Jan 2005 17:16:45 +0100 From: Ingo Molnar To: William Lee Irwin III Cc: Esben Nielsen , Rui Nuno Capela , "K.R. Foley" , Fernando Lopez-Lezcano , mark_h_johnson@raytheon.com, Amit Shah , Karsten Wiese , Bill Huey , Adam Heath , emann@mrv.com, Gunther Persoons , linux-kernel@vger.kernel.org, Florian Schmidt , Lee Revell , Shane Shrybman , Thomas Gleixner , Michal Schmidt Subject: Re: Real-time rw-locks (Re: [patch] Real-Time Preemption, -RT-2.6.10-rc2-mm3-V0.7.32-15) Message-ID: <20050128161645.GA17216@elte.hu> References: <20041214113519.GA21790@elte.hu> <20050128073856.GA2186@elte.hu> <20050128115640.GP10843@holomorphy.com> <20050128152802.GA15508@elte.hu> <20050128155549.GR10843@holomorphy.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20050128155549.GR10843@holomorphy.com> User-Agent: Mutt/1.4.1i X-ELTE-SpamVersion: MailScanner 4.31.6-itk1 (ELTE 1.2) SpamAssassin 2.63 ClamAV 0.73 X-ELTE-VirusStatus: clean X-ELTE-SpamCheck: no X-ELTE-SpamCheck-Details: score=-4.9, required 5.9, autolearn=not spam, BAYES_00 -4.90 X-ELTE-SpamLevel: X-ELTE-SpamScore: -4 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1413 Lines: 31 * William Lee Irwin III wrote: > The performance relative to mutual exclusion is quantifiable and very > reproducible. [...] yes, i dont doubt the results - my point is that it's not proven that the other, more read-friendly types of locking underperform rwlocks. Obviously spinlocks and rwlocks have the same cache-bounce properties, so rwlocks can outperform spinlocks if the read path overhead is higher than that of a bounce, and reads are dominant. But it's still a poor form of scalability. In fact, when the read path is really expensive (larger than say 10-20 usecs) an rwlock can produce the appearance of linear scalability, when compared to spinlocks. > As far as performance relative to RCU goes, I suspect cases where > write-side latency is important will arise for these. Other lockless > methods are probably more appropriate, and are more likely to dominate > rwlocks as expected. For instance, a reimplementation of the radix > trees for lockless insertion and traversal (c.f. lockless pagetable > patches for examples of how that's carried out) is plausible, where > RCU memory overhead in struct page is not. yeah. 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/