Re: [Linuxarm] Re: [PATCH for-next 00/32] spin lock usage optimization for SCSI drivers

Xiaofei Tan
2021-02-18T08:07:27Z

Hi Finn,

On 2021/2/9 13:06, Finn Thain wrote:
> On Tue, 9 Feb 2021, Song Bao Hua (Barry Song) wrote:
>
>>> -----Original Message-----
>>> From: Finn Thain [mailto:fthain@telegraphics.com.au]
>>> Sent: Monday, February 8, 2021 8:57 PM
>>> To: tanxiaofei <tanxiaofei@huawei.com>
>>> Cc: jejb@linux.ibm.com; martin.petersen@oracle.com;
>>> linux-scsi@vger.kernel.org; linux-kernel@vger.kernel.org;
>>> linuxarm@openeuler.org
>>> Subject: [Linuxarm] Re: [PATCH for-next 00/32] spin lock usage optimization
>>> for SCSI drivers
>>>
>>> On Sun, 7 Feb 2021, Xiaofei Tan wrote:
>>>
>>>> Replace spin_lock_irqsave with spin_lock in hard IRQ of SCSI drivers.
>>>> There are no function changes, but may speed up if interrupt happen too
>>>> often.
>>>
>>> This change doesn't necessarily work on platforms that support nested
>>> interrupts.
>>>
>>> Were you able to measure any benefit from this change on some other
>>> platform?
>>
>> I think the code disabling irq in hardIRQ is simply wrong.
>> Since this commit
>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=e58aa3d2d0cc
>> genirq: Run irq handlers with interrupts disabled
>>
>> interrupt handlers are definitely running in a irq-disabled context
>> unless irq handlers enable them explicitly in the handler to permit
>> other interrupts.
>>
>
> Repeating the same claim does not somehow make it true. If you put your
> claim to the test, you'll see that that interrupts are not disabled on
> m68k when interrupt handlers execute.
>
> The Interrupt Priority Level (IPL) can prevent any given irq handler from
> being re-entered, but an irq with a higher priority level may be handled
> during execution of a lower priority irq handler.
>
> sonic_interrupt() uses an irq lock within an interrupt handler to avoid
> issues relating to this. This kind of locking may be needed in the drivers
> you are trying to patch. Or it might not. Apparently, no-one has looked.
>

According to your discussion with Barry, it seems that m68k is a little
different from other architecture, and this kind of modification of this
patch cannot be applied to m68k. So, could help to point out which
driver belong to m68k architecture in this patch set of SCSI?
I can remove them.

BTW, sonic_interrupt() is from net driver natsemi, right? It would be
appreciative if only discuss SCSI drivers in this patch set. thanks.

> .
>