linux-kernel - Re: [PATCH] scsi: ufs: core: move some irq handling back to hardirq (with time limit)

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Message-ID: <53bfd619-4066-4dcb-b3f0-d04177e05355@linaro.org>
Date: Thu, 24 Jul 2025 13:54:46 +0200
From: Neil Armstrong <neil.armstrong@...aro.org>
To: André Draszik <andre.draszik@...aro.org>,
 Alim Akhtar <alim.akhtar@...sung.com>, Avri Altman <avri.altman@....com>,
 Bart Van Assche <bvanassche@....org>,
 "James E.J. Bottomley" <James.Bottomley@...senPartnership.com>,
 "Martin K. Petersen" <martin.petersen@...cle.com>
Cc: Peter Griffin <peter.griffin@...aro.org>,
 Tudor Ambarus <tudor.ambarus@...aro.org>,
 Will McVicker <willmcvicker@...gle.com>,
 Manivannan Sadhasivam <mani@...nel.org>, kernel-team@...roid.com,
 linux-arm-msm@...r.kernel.org, linux-scsi@...r.kernel.org,
 linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] scsi: ufs: core: move some irq handling back to hardirq
 (with time limit)

On 24/07/2025 13:44, André Draszik wrote:
> On Thu, 2025-07-24 at 10:54 +0100, André Draszik wrote:
>> fio results on Pixel 6:
>>    read / 1 job     original    after    this commit
>>      min IOPS        4,653.60   2,704.40    3,902.80
>>      max IOPS        6,151.80   4,847.60    6,103.40
>>      avg IOPS        5,488.82   4,226.61    5,314.89
>>      cpu % usr           1.85       1.72        1.97
>>      cpu % sys          32.46      28.88       33.29
>>      bw MB/s            21.46      16.50       20.76
>>
>>    read / 8 jobs    original    after    this commit
>>      min IOPS       18,207.80  11,323.00   17,911.80
>>      max IOPS       25,535.80  14,477.40   24,373.60
>>      avg IOPS       22,529.93  13,325.59   21,868.85
>>      cpu % usr           1.70       1.41        1.67
>>      cpu % sys          27.89      21.85       27.23
>>      bw MB/s            88.10      52.10       84.48
>>
>>    write / 1 job    original    after    this commit
>>      min IOPS        6,524.20   3,136.00    5,988.40
>>      max IOPS        7,303.60   5,144.40    7,232.40
>>      avg IOPS        7,169.80   4,608.29    7,014.66
>>      cpu % usr           2.29       2.34        2.23
>>      cpu % sys          41.91      39.34       42.48
>>      bw MB/s            28.02      18.00       27.42
>>
>>    write / 8 jobs   original    after    this commit
>>      min IOPS       12,685.40  13,783.00   12,622.40
>>      max IOPS       30,814.20  22,122.00   29,636.00
>>      avg IOPS       21,539.04  18,552.63   21,134.65
>>      cpu % usr           2.08       1.61        2.07
>>      cpu % sys          30.86      23.88       30.64
>>      bw MB/s            84.18      72.54       82.62
> 
> Given the severe performance drop introduced by the culprit
> commit, it might make sense to instead just revert it for
> 6.16 now, while this patch here can mature and be properly
> reviewed. At least then 6.16 will not have any performance
> regression of such a scale.

The original change was designed to stop the interrupt handler
to starve the system and create display artifact and cause
timeouts on system controller submission. While imperfect,
it would require some fine tuning for smaller controllers
like on the Pixel 6 that when less queues.

Neil

> 
> Cheers,
> Andre'