From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Tue, 24 Nov 2020 01:13:50 +0100 From: Frederic Weisbecker Subject: Re: [patch 14/19] softirq: Make softirq control and processing RT aware Message-ID: <20201124001350.GF1751@lothringen> References: <20201113140207.499353218@linutronix.de> <20201113141734.324061522@linutronix.de> <20201123134437.GA95787@lothringen> <87r1ojnaai.fsf@nanos.tec.linutronix.de> <20201123235801.GE1751@lothringen> <87wnyblitk.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <87wnyblitk.fsf@nanos.tec.linutronix.de> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-um" Errors-To: linux-um-bounces+geert=linux-m68k.org@lists.infradead.org To: Thomas Gleixner Cc: Rich Felker , Catalin Marinas , Paul McKenney , Arnd Bergmann , linux-sh@vger.kernel.org, Peter Zijlstra , Richard Weinberger , Sebastian Andrzej Siewior , Valentin Schneider , Jeff Dike , LKML , Yoshinori Sato , "James E.J. Bottomley" , linux-parisc@vger.kernel.org, Marc Zyngier , Russell King , linux-um@lists.infradead.org, Will Deacon , Helge Deller , linux-arm-kernel@lists.infradead.org, Anton Ivanov On Tue, Nov 24, 2020 at 01:06:15AM +0100, Thomas Gleixner wrote: > On Tue, Nov 24 2020 at 00:58, Frederic Weisbecker wrote: > > On Mon, Nov 23, 2020 at 08:27:33PM +0100, Thomas Gleixner wrote: > >> On Mon, Nov 23 2020 at 14:44, Frederic Weisbecker wrote: > >> > On Fri, Nov 13, 2020 at 03:02:21PM +0100, Thomas Gleixner wrote: > >> >> + /* > >> >> + * Adjust softirq count to SOFTIRQ_OFFSET which makes > >> >> + * in_serving_softirq() become true. > >> >> + */ > >> >> + cnt = SOFTIRQ_OFFSET; > >> >> + __local_bh_enable(cnt, false); > >> > > >> > But then you enter __do_softirq() with softirq_count() == SOFTIRQ_OFFSET. > >> > __do_softirq() calls softirq_handle_begin() which then sets it back to > >> > SOFTIRQ_DISABLE_OFFSET... > >> > >> The RT variant of it added in this very same patch > >> > +static inline void softirq_handle_begin(void) { } > >> > +static inline void softirq_handle_end(void) { } > > > > Ah but then account_irq_enter_time() is called with SOFTIRQ_OFFSET (it's > > currently called with softirq_count == 0 at this point) and that may mess > > up irqtime accounting which relies on it. It could spuriously account all > > the time between the last (soft-)IRQ exit until now as softirq time. > > Good point. Haven't thought about that. Let me have a look again. But I'm cooking a patchset which moves account_irq_enter_time() after HARDIRQ_OFFSET or SOFTIRQ_OFFSET is incremented. This will allow us to move tick_irq_enter() under this layout: preempt_count_add(HARDIRQ_OFFSET) lockdep_hardirq_enter() tick_irq_enter() account_irq_enter_time() This way tick_irq_enter() can be correctly handled by lockdep and we can remove the nasty hack which temporarily disables softirqs around it. And as a side effect it should also fix your issue. I should have that ready soonish. Thanks. _______________________________________________ linux-um mailing list linux-um@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-um