From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261848AbVAHVyj (ORCPT ); Sat, 8 Jan 2005 16:54:39 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261834AbVAHVyA (ORCPT ); Sat, 8 Jan 2005 16:54:00 -0500 Received: from fw.osdl.org ([65.172.181.6]:38335 "EHLO mail.osdl.org") by vger.kernel.org with ESMTP id S261894AbVAHVwG (ORCPT ); Sat, 8 Jan 2005 16:52:06 -0500 Date: Sat, 8 Jan 2005 13:51:46 -0800 (PST) From: Linus Torvalds To: Lee Revell cc: Chris Friesen , Mike Waychison , Alan Cox , Oleg Nesterov , William Lee Irwin III , Linux Kernel Mailing List Subject: Re: Make pipe data structure be a circular list of pages, rather than In-Reply-To: <1105220326.24592.98.camel@krustophenia.net> Message-ID: References: <41DE9D10.B33ED5E4@tv-sign.ru> <1105113998.24187.361.camel@localhost.localdomain> <41DEF81B.60905@sun.com> <41DF1F3D.3030006@nortelnetworks.com> <1105220326.24592.98.camel@krustophenia.net> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 8 Jan 2005, Lee Revell wrote: > > Many latency critical apps use (tmpfs mounted) FIFO's for IPC; the Linux > FIFO being one of the fastest known IPC mechanisms. Each client in the > JACK (http://jackit.sf.net) graph wakes the next one by writing a single > byte to a FIFO. Ardour's GUI, control, and audio threads interact via a > similar mechanism. How would you expect this change to impact the inter > thread wakeup latency? It's confusing when people say "performance", > meaning "increased throughput albeit with more latency". For many > people that's a regression. I posted the performance numbers in the thread already, and with every single throughput number I also talked abotu what the latency difference was. So quite frankly, if you were confused, I suspect it was because you didn't read them. Tssk, tssk. Short and sweet: the latency changes are in the noise for SMP, but can be seen on UP. I'll look at it a bit more: since I had to add the coalescing code anyway, I might also decide to re-use a buffer page rather than free it immediately, since that may help latency for small writes. Linus