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Message-ID: <5be7a006-054d-4275-9c83-2687461028ef@linaro.org>
Date: Thu, 27 Mar 2025 13:47:47 +0100
From: Neil Armstrong <neil.armstrong@...aro.org>
To: Bart Van Assche <bvanassche@....org>,
Alim Akhtar <alim.akhtar@...sung.com>, Avri Altman <avri.altman@....com>,
"James E.J. Bottomley" <James.Bottomley@...senPartnership.com>,
"Martin K. Petersen" <martin.petersen@...cle.com>
Cc: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
linux-arm-msm@...r.kernel.org, linux-scsi@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC v2 2/2] ufs: core: delegate the interrupt service
routine to a threaded irq handler
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.
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