From mboxrd@z Thu Jan 1 00:00:00 1970 From: sboyd@codeaurora.org (Stephen Boyd) Date: Fri, 08 Nov 2013 13:53:32 -0800 Subject: [PATCH] ARM: Support arch_irq_work_raise() via self IPIs In-Reply-To: References: <526DBEAA.4030707@linaro.org> <1382984701-2371-1-git-send-email-sboyd@codeaurora.org> <878uxcq1m7.fsf@linaro.org> <20131029060058.GD21983@codeaurora.org> Message-ID: <527D5D5C.2080409@codeaurora.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 11/08/13 12:45, Olof Johansson wrote: > On Fri, Nov 8, 2013 at 12:06 PM, Olof Johansson wrote: >> On Mon, Oct 28, 2013 at 11:00 PM, Stephen Boyd wrote: >>> On 10/28, Kevin Hilman wrote: >>>> Stephen Boyd writes: >>>> >>>>> This will allow the scheduler tick to be restarted if we're in >>>>> full NOHZ mode. >>>>> >>>>> Cc: Kevin Hilman >>>>> Cc: Frederic Weisbecker >>>>> Signed-off-by: Stephen Boyd >>>> Minor nit, but I'd prefer a more verbose changelog (I forget things >>>> quickly and like to rely on changelogs for my memory.) Probably worth >>>> adding something like: "By default, irq_work is tied to the tick >>>> processing (update_process_times()) but in full NOHZ mode, no tick means >>>> no IRQ work. In order for IRQ work to be done in full NOHZ mode, a >>>> self-IPI is used to process IRQ work." >>>> >>>> Other than the changelog nit, patch looks good, feel free to add >>>> >>>> Reviewed-by: Kevin Hilman >>>> >>>> If Russell is OK with this, it can go to his patch system. >>>> >>> Fair enough. This is what I came up with. I'll send it off to the >>> patch tracker in about 12 hours if nobody else has anymore >>> comments. >>> >>> ----8<----- >>> ARM: Support arch_irq_work_raise() via self IPIs >>> >>> By default, IRQ work is run from the tick interrupt (see >>> irq_work_run() in update_process_times()). When we're in full >>> NOHZ mode, restarting the tick requires the use of IRQ work and >>> if the only place we run IRQ work is in the tick interrupt we >>> have an unbreakable cycle. Implement arch_irq_work_raise() via >>> self IPIs to break this cycle and get the tick started again. >>> Note that we implement this via IPIs which are only available on >>> SMP builds. This shouldn't be a problem because full NOHZ is only >>> supported on SMP builds anyway. >>> >>> Signed-off-by: Stephen Boyd >>> Reviewed-by: Kevin Hilman >>> Cc: Frederic Weisbecker >> >> Hm, so I think this just landed in -next, which seems... late for >> 3.13. Anyway, it causes boot failures on Cubieboards (Allwinner A10), >> I just bisected it down to this patch (fails to boot >> multi_v7_defconfig, no console output at all). >> >> Unfortunately I'm not getting any debug_ll output from the board at >> the moment, so I can't actually get to a panic stack or other error >> info. :( I hope I can get back to you with one later today. > Turns out that I hit this on the BeagleBone as well, and I got a trace > out of it. Seems like this might be broken on all non-SMP platforms > built with CONFIG_SMP=y? Ah yes. We don't have IPI support on UP kernels but SMP_ON_UP exposes arch_irq_work_raise(). How about this? We should just skip this function if we're running on UP. ---8<---- diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c index bf9a0d6d..e115cbb 100644 --- a/arch/arm/kernel/smp.c +++ b/arch/arm/kernel/smp.c @@ -453,7 +453,8 @@ void arch_send_call_function_single_ipi(int cpu) #ifdef CONFIG_IRQ_WORK void arch_irq_work_raise(void) { - smp_cross_call(cpumask_of(smp_processor_id()), IPI_IRQ_WORK); + if (is_smp()) + smp_cross_call(cpumask_of(smp_processor_id()), IPI_IRQ_WORK); } #endif -- Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation