Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Sun, 1 Apr 2001 05:05:41 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Sun, 1 Apr 2001 05:05:32 -0400 Received: from colorfullife.com ([216.156.138.34]:11528 "EHLO colorfullife.com") by vger.kernel.org with ESMTP id ; Sun, 1 Apr 2001 05:05:24 -0400 Message-ID: <3AC6559E.575C4BAA@colorfullife.com> Date: Sun, 01 Apr 2001 00:09:34 +0200 From: Manfred Spraul X-Mailer: Mozilla 4.76 [en] (X11; U; Linux 2.4.2-ac20 i686) X-Accept-Language: en, de MIME-Version: 1.0 To: Pavel Machek CC: linux-kernel@vger.kernel.org Subject: Re: Serial port latency In-Reply-To: <000401c0b319517fea9@local> <20010325231013.A34@(none)> <000401c0b828$bbdf7380$5517fea9@local> <20010331003645.F1579@atrey.karlin.mff.cuni.cz> Content-Type: multipart/mixed; boundary="------------3736C7F42ABF3E1F14E70CD9" Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org This is a multi-part message in MIME format. --------------3736C7F42ABF3E1F14E70CD9 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Pavel Machek wrote: > > > > > > > I've seen similar bugs. If you hook something on schedule_tq and > > forget > > > to set current->need_resched, this is exactly what you get. > > > > > I'm running with a patch that printk's if cpu_idle() is called while a > > softirq is pending. > > If I access the floppy on my K6/200 every track triggers the check, and > > sometimes the console blanking code triggers it. > > Seems floppy and console is buggy, then. > No. The softirq implementation is buggy. I can trigger the problem with the TASKLET_HI (floppy), and both net rx and tx (ping -l) > > What about creating a special cpu_is_idle() function that the idle > > functions must call before sleeping? > > I'd say just fix all the bugs. > Ok, there are 2 bugs that are (afaics) impossible to fix without checking for pending softirq's in cpu_idle(): a) queue_task(my_task1, tq_immediate); mark_bh(); schedule(); ;within schedule: do_softirq() ;within my_task1: mark_bh(); ; bh returns, but do_softirq won't loop ; do_softirq returns. ; schedule() clears current->need_resched ; idle thread scheduled. --> idle can run although softirq's are pending I assume I trigger this race with the floppy driver. b) hw interrupt do_softirq within the net_rx handler: another hw interrupt, additional packets are queued do_softirq won't loop. returns to idle thread. --> packets delayed unnecessary. What about the attached patch? Obviously the other idle cpu must be converted to use the function as well. -- Manfred --------------3736C7F42ABF3E1F14E70CD9 Content-Type: text/plain; charset=us-ascii; name="patch-proc" Content-Transfer-Encoding: 7bit Content-Disposition: inline; filename="patch-proc" --- 2.4/arch/i386/kernel/process.c Thu Feb 22 22:28:52 2001 +++ build-2.4/arch/i386/kernel/process.c Sun Apr 1 00:05:21 2001 @@ -73,6 +73,30 @@ hlt_counter--; } +/** + * cpu_is_idle - helper function for idle functions + * + * pm_idle functions must call this function to verify that + * the cpu is really idle. It must be called with disabled + * local interrupts. + * Return values: + * 0: cpu was not idle, local interrupts reenabled. + * 1: go into power saving mode, local interrupts are + * still disabled. +*/ +static inline int cpu_is_idle(void) +{ + if (current->need_resched) { + __sti(); + return 0; + } + if (softirq_active(smp_processor_id()) & softirq_mask(smp_processor_id())) { + __sti(); + do_softirq(); + return 0; + } + return 1; +} /* * We use this if we don't have any better * idle routine.. @@ -81,10 +105,8 @@ { if (current_cpu_data.hlt_works_ok && !hlt_counter) { __cli(); - if (!current->need_resched) + if (cpu_is_idle()) safe_halt(); - else - __sti(); } } --------------3736C7F42ABF3E1F14E70CD9-- - 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/