Re: [PATCH RFC v2 2/2] ufs: core: delegate the interrupt service routine to a threaded irq handler

[Neil Armstrong <neil.armstrong@linaro.org>]

Hi,

On 27/03/2025 12:56, Bart Van Assche wrote:
> On 3/26/25 4:36 AM, Neil Armstrong wrote:
>  > When MCQ & Interrupt Aggregation are supported, the interrupt
>  > are directly handled in the "hard" interrupt routine to
>  > keep IOPs high since queues handling is done in separate
>  > per-queue interrupt routines.
> 
> The above explanation suggests that I/O completions are handled by the
> modified interrupt handler. This is not necessarily the case. With MCQ,
> I/O completions are either handled by dedicated interrupts or by the
> legacy interrupt handler.

Will update the sentence with that

> 
>> Reported bandwidth is not affected on various tests.
> 
> This kind of patch can only affect command completion latency but not
> the bandwidth, isn't it?

Yes, but on a fully loaded system, it will enhance bandwidth
but with a greater latency, but without eating irq handling time
for other routines.

> 
>> +/**
>> + * ufshcd_intr - Main interrupt service routine
>> + * @irq: irq number
>> + * @__hba: pointer to adapter instance
>> + *
>> + * Return:
>> + *  IRQ_HANDLED     - If interrupt is valid
>> + *  IRQ_WAKE_THREAD - If handling is moved to threaded handled
>> + *  IRQ_NONE        - If invalid interrupt
>> + */
>> +static irqreturn_t ufshcd_intr(int irq, void *__hba)
>> +{
>> +    struct ufs_hba *hba = __hba;
>> +
>> +    /*
>> +     * Move interrupt handling to thread when MCQ is not supported
>> +     * or when Interrupt Aggregation is not supported, leading to
>> +     * potentially longer interrupt handling.
>> +     */
>> +    if (!is_mcq_supported(hba) || !ufshcd_is_intr_aggr_allowed(hba))
>> +        return IRQ_WAKE_THREAD;
>> +
>> +    /* Directly handle interrupts since MCQ handlers does the hard job */
>> +    return ufshcd_sl_intr(hba, ufshcd_readl(hba, REG_INTERRUPT_STATUS) &
>> +                   ufshcd_readl(hba, REG_INTERRUPT_ENABLE));
>> +}
> 
> Where has ufshcd_is_intr_aggr_allowed() been defined? I can't find this
> function.

It's in include/ufs/ufshcd.h

> 
> For the MCQ case, this patch removes the loop from around
> ufshcd_sl_intr() without explaining in the patch description why this change has been made. Please explain all changes in the patch
> description.

Ack will update explaining this change.

Thanks,
Neil

> 
> Thanks,
> 
> Bart.