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Subject: Re: [PATCH v3 1/3] irqchip/loongson-eiointc: Skip handling if there
 is no pending irq
To: Huacai Chen <chenhuacai@kernel.org>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>,
 Thomas Gleixner <tglx@linutronix.de>, linux-mips@vger.kernel.org,
 linux-kernel@vger.kernel.org, Sergey Shtylyov <s.shtylyov@omp.ru>,
 lvjianmin@loongson.cn
References: <20240118121542.748351-1-maobibo@loongson.cn>
 <20240118121542.748351-2-maobibo@loongson.cn>
 <CAAhV-H5-da4AvtgHu1Hv0sbXddab6Mqg6eCkwJzr32Xi4A97yQ@mail.gmail.com>
From: maobibo <maobibo@loongson.cn>
Message-ID: <8c133026-3c70-2e2a-7f79-2f3c4327b7b4@loongson.cn>
Date: Wed, 24 Jan 2024 18:02:10 +0800
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On 2024/1/24 下午5:51, Huacai Chen wrote:
> Hi, Bibo,
> 
> On Thu, Jan 18, 2024 at 8:15 PM Bibo Mao <maobibo@loongson.cn> wrote:
>>
>> There is one simple optimization in the interrupt dispatch function
>> eiointc_irq_dispatch. There are 256 IRQs supported for eiointc, eiointc
>> irq handler reads the bitmap and find pending irqs when irq happens.
>> So there are four times of consecutive iocsr_read64 operations for the
>> total 256 bits to find all pending irqs. If the pending bitmap is zero,
>> it means that there is no pending irq for the this irq bitmap range,
>> we can skip handling to avoid some useless operations such as clearing
>> hw ISR.
>>
>> Signed-off-by: Bibo Mao <maobibo@loongson.cn>
>> ---
>>   drivers/irqchip/irq-loongson-eiointc.c | 11 +++++++++++
>>   1 file changed, 11 insertions(+)
>>
>> diff --git a/drivers/irqchip/irq-loongson-eiointc.c b/drivers/irqchip/irq-loongson-eiointc.c
>> index 1623cd779175..6143adb1b73b 100644
>> --- a/drivers/irqchip/irq-loongson-eiointc.c
>> +++ b/drivers/irqchip/irq-loongson-eiointc.c
>> @@ -198,6 +198,17 @@ static void eiointc_irq_dispatch(struct irq_desc *desc)
>>
>>          for (i = 0; i < eiointc_priv[0]->vec_count / VEC_COUNT_PER_REG; i++) {
>>                  pending = iocsr_read64(EIOINTC_REG_ISR + (i << 3));
>> +
>> +               /*
>> +                * Get pending eiointc irq from bitmap status, there are 4 times
>> +                * consecutive iocsr_read64 operations for 256 IRQs.
>> +                *
>> +                * Skip handling if pending bitmap is zero
> This driver is shared by Loongson-2 and Loongson-3 series, for
> Loongson-2K0500 there is only 128 IRQs, so I suggest only keep the
> last line "Skip handling if current pending bitmap is zero" is enough.
Sure, will refine the patch in this way.

Regards
Bibo Mao
> 
> Huacai
> 
>> +                */
>> +               if (!pending)
>> +                       continue;
>> +
>> +               /* Clear the IRQs */
>>                  iocsr_write64(pending, EIOINTC_REG_ISR + (i << 3));
>>                  while (pending) {
>>                          int bit = __ffs(pending);
>> --
>> 2.39.3
>>