From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ingo Molnar Subject: Re: [patch 1/4] - Potential performance bottleneck for Linxu TCP Date: Thu, 30 Nov 2006 07:47:58 +0100 Message-ID: <20061130064758.GD2003@elte.hu> References: <2f14bf623344.456de60a@fnal.gov> <20061129.181950.31643130.davem@davemloft.net> <20061130061758.GA2003@elte.hu> <20061129.223055.05159325.davem@davemloft.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: wenji@fnal.gov, akpm@osdl.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Return-path: Received: from mx2.mail.elte.hu ([157.181.151.9]:49821 "EHLO mx2.mail.elte.hu") by vger.kernel.org with ESMTP id S1758001AbWK3GuL (ORCPT ); Thu, 30 Nov 2006 01:50:11 -0500 To: David Miller Content-Disposition: inline In-Reply-To: <20061129.223055.05159325.davem@davemloft.net> Sender: netdev-owner@vger.kernel.org List-Id: netdev.vger.kernel.org * David Miller wrote: > > yeah, i like this one. If the problem is "too long locked section", > > then the most natural solution is to "break up the lock", not to > > "boost the priority of the lock-holding task" (which is what the > > proposed patch does). > > Ingo you're mis-read the problem :-) yeah, the problem isnt too long locked section but "too much time spent holding a lock" and hence opening up ourselves to possible negative side-effects of the scheduler's fairness algorithm when it forces a preemption of that process context with that lock held (and forcing all subsequent packets to be backlogged). but please read my last mail - i think i'm slowly starting to wake up ;-) I dont think there is any real problem: a tweak to the scheduler that in essence gives TCP-using tasks a preference changes the balance of workloads. Such an explicit tweak is possible already. furthermore, the tweak allows the shifting of processing from a prioritized process context into a highest-priority softirq context. (it's not proven that there is any significant /net win/ of performance: all that was proven is that if we shift TCP processing from process context into softirq context then TCP throughput of that otherwise penalized process context increases.) Ingo