On Thursday 10 December 2015 08:46 PM, Sekhar Nori wrote:
> Hi Felipe,
>
> On Tuesday 08 December 2015 07:15 PM, Felipe Balbi wrote:
>> Sekhar Nori <nsekhar@xxxxxx> writes:
>
>>> + /*
>>> + * A spurious IRQ can result if interrupt that triggered the
>>> + * sorting is no longer active during the sorting (10 INTC
>>> + * functional clock cycles after interrupt assertion). Or a
>>> + * change in interrupt mask affected the result during sorting
>>> + * time. There is no special handling required except ignoring
>>> + * the SIR register value just read and retrying.
>>> + * See section 6.2.5 of AM335x TRM Literature Number: SPRUH73K
>>> + *
>>> + * Many a times, a spurious interrupt situation has been fixed
>>> + * by adding a flush for the posted write acking the IRQ in
>>> + * the device driver. Typically, this is going be the device
>>> + * driver whose interrupt was handled just before the spurious
>>> + * IRQ occurred. Pay attention to those device drivers if you
>>> + * run into hitting the spurious IRQ condition below.
>>> + */
>>> + if ((irqnr & SPURIOUSIRQ_MASK) == SPURIOUSIRQ_MASK) {
>>
>> sounds like unlikely() wouldn't hurt here.
>
> I can add, but looks like it does not make a big difference. See below.
>
>>
>>> + pr_err_once("%s: spurious irq!\n", __func__);
>>> + irq_err_count++;
>>> + omap_ack_irq(NULL);
>>> + return;
>>> + }
>>> +
>>> irqnr &= ACTIVEIRQ_MASK;
>>> - WARN_ONCE(!irqnr, "Spurious IRQ ?\n");
>>> handle_domain_irq(domain, irqnr, regs);
>>
>> care to run kernel function profiler against omap_intc_handle_irq()
>> before and after this patch ?
>
> Before this patch I see average running time time of 34us. That
> increases to 37.8us after this patch. With unlikely() the number I got
> was 37.4us. So the benefit with unlikely() is in the noise range.
>
> This was using AM335x EVM at 720 MHz.
Just sent a v3 with unlikely() and profiling information added to commit
message.
Thanks,
Sekhar
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