From mboxrd@z Thu Jan 1 00:00:00 1970 From: magnus.damm@gmail.com (Magnus Damm) Date: Thu, 29 Aug 2013 17:41:55 +0900 Subject: [PATCH] clocksource: em_sti: Adjust clock event rating to fix SMP broadcast In-Reply-To: <51F9777B.2080500@codeaurora.org> References: <1375251940-7809-1-git-send-email-horms+renesas@verge.net.au> <51F94A35.2020907@codeaurora.org> <51F9777B.2080500@codeaurora.org> Message-ID: To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Thu, Aug 1, 2013 at 5:45 AM, Stephen Boyd wrote: > On 07/31/13 12:17, Magnus Damm wrote: >> Hi Stephen, >> >> On Thu, Aug 1, 2013 at 2:32 AM, Stephen Boyd wrote: >>> On 07/30/13 23:25, Simon Horman wrote: >>>> From: Magnus Damm >>>> >>>> Update the STI rating from 200 to 80 to fix SMP operation with >>>> the ARM broadcast timer. This breakage was introduced by: >>>> >>>> f7db706 ARM: 7674/1: smp: Avoid dummy clockevent being preferred over real hardware clock-event >>>> >>>> Without this fix SMP operation is broken on EMEV2 since no >>>> broadcast timer interrupts trigger on the secondary CPU cores. >>>> >>>> Signed-off-by: Magnus Damm >>>> Signed-off-by: Simon Horman >>>> --- >>> This looks suspicious. Are you're purposefully deflating the rating so >>> that the STI timer fills in the broadcast position? Why not make the STI >>> cpumask be all possible CPUs? Presumably the interrupt can target all >>> CPUs since it isn't a per-cpu interrupt and doing this would cause the >>> STI to fill in the broadcast slot, leaving the per-cpu dummys in the >>> tick position. >> While letting the timer broadcast to all CPUs sounds interesting the >> STI driver has so far only been used to drive a single CPU core. This >> used to work well for us but has since some time unfortunately been >> broken. I agree that it may be suboptimal with a single timer like STI >> and using IPI for broadcast, but for more efficient SMP we already >> have TWD or arch timer. > > I think there is some confusion. The mask field says what CPUs the timer > can possibly interrupt and for non-percpu interrupts this should be all > possible CPUs (unless we're talking clusters, etc. but I don't think we > are). Can you please give the output of /proc/timer_list or confirm that > the STI is your broadcast source? If so you should probably be marking > the cpumask for all possible CPUs so that the clockevent core knows to > prefer this clockevent for the broadcast source and not a per-cpu > source. Then you can leave the rating as is. Hello Stephen, Thanks for your suggestion. Yes, there was indeed some confusion. Now after diving into the code a bit deeper I can finally understand what you mean. Instead of adjusting the rating I've changed the cpumask member like this: --- 0001/drivers/clocksource/em_sti.c +++ work/drivers/clocksource/em_sti.c 2013-08-29 17:33:16.000000000 +0900 @@ -301,7 +301,7 @@ static void em_sti_register_clockevent(s ced->name = dev_name(&p->pdev->dev); ced->features = CLOCK_EVT_FEAT_ONESHOT; ced->rating = 200; - ced->cpumask = cpumask_of(0); + ced->cpumask = cpu_all_mask; ced->set_next_event = em_sti_clock_event_next; ced->set_mode = em_sti_clock_event_mode; Without the cpumask fix or without the earlier rating fix the following interrupt count can be seen in /proc/interrupts on KZM9D: 157: 140 0 GIC 157 e0180000.sti 160: 0 0 e0050000.gpio 1 eth0 IPI0: 0 0 CPU wakeup interrupts IPI1: 0 0 Timer broadcast interrupts Above, notice how no IPI1 interrupts seem to be arriving. With the cpumask fix above the interrupt count becomes like this: 157: 559 0 GIC 157 e0180000.sti 160: 0 0 e0050000.gpio 1 eth0 IPI0: 0 0 CPU wakeup interrupts IPI1: 0 601 Timer broadcast interrupts Would this be in line with your expectation? Thanks, / magnus