Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S263104AbVD3A40 (ORCPT ); Fri, 29 Apr 2005 20:56:26 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S263105AbVD3A4Z (ORCPT ); Fri, 29 Apr 2005 20:56:25 -0400 Received: from fsmlabs.com ([168.103.115.128]:60117 "EHLO fsmlabs.com") by vger.kernel.org with ESMTP id S263104AbVD3A4H (ORCPT ); Fri, 29 Apr 2005 20:56:07 -0400 Date: Fri, 29 Apr 2005 18:58:46 -0600 (MDT) From: Zwane Mwaikambo To: Venkatesh Pallipadi cc: Andrew Morton , Linus Torvalds , mingo@elte.hu, linux-kernel , Rajesh Shah , John Stultz , Andi Kleen , Asit K Mallick Subject: Re: [RFC][PATCH] i386 x86-64 Eliminate Local APIC timer interrupt In-Reply-To: Message-ID: References: <20050429172605.A23722@unix-os.sc.intel.com> 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 Content-Length: 1597 Lines: 36 On Fri, 29 Apr 2005, Zwane Mwaikambo wrote: > On Fri, 29 Apr 2005, Venkatesh Pallipadi wrote: > > > > > Background: > > Local APIC timer stops functioning when CPU is in C3 state. As a > > result the local APIC timer interrupt will fire at uncertain times, depending > > on how long we spend in C3 state. And this has two side effects > > * Idle balancing will not happen as we expect it to. > > * Kernel statistics for idle time will not be proper (as we get less LAPIC > > interrupts when we are idle). This can result in confusing other parts of > > kernel (like ondemand cpufreq governor) which depends on this idle stats. > > > > > > Proposed Fix: > > Attached is a prototype patch, that tries to eliminate the dependency on > > local APIC timer for update_process_times(). The patch gets rid of Local APIC > > timer altogether. We use the timer interrupt (IRQ 0) configured in > > broadcast mode in IOAPIC instead (Doesn't work with 8259). > > As changing anything related to basic timer interrupt is a little bit risky, > > I have a boot parameter currently ("useapictimer") to switch back to original > > local APIC timer way of doing things. > > This all looks like it'll contend on irq0 related locks really badly, have > you profiled this? Hmm ok i see you have IRQ_PER_CPU, so please ignore my statement. Thanks, Zwane - 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/