Re: [PATCH V1] ufs: core: Fix interrupt handling for MCQ Mode in ufshcd_intr

["Peter Wang (王信友)" <peter.wang@mediatek.com>]

On Wed, 2025-07-30 at 09:04 -0700, Bart Van Assche wrote:
> 
> Hi Peter,
> 
> Thanks for having taken a look but I think that you misunderstood my
> patch. My patch does not modify the behavior of the UFS driver on
> systems using the legacy single doorbell mode. It only modifies the
> behavior on systems supporting MCQ. And on systems that support MCQ,
> it
> restores the behavior from before when commit 3c7ac40d7322 ("scsi:
> ufs:
> core: Delegate the interrupt service routine to a threaded IRQ
> handler")
> got merged.
> 
> On MCQ systems, if the completion interrupt is processed by the CPU
> core
> that submitted the I/O, then I/O workloads are self-regulating. The
> more
> time that is spent in the completion interrupt handler, the more the
> submitter will be slowed down. This is not the case in legacy single
> doorbell mode since when using that mode all completion interrupts
> are
> processed by a single CPU core.
> 
> Bart.


Hi Bart,

I am fully agree that your patch is 100% correct.

But what I want to express is that this is a patch
that makes me feel confused about the code.
Originally, ufshcd_intr moved some heavy (legacy) work
to ufshcd_threaded_intr because those work could take
a long time to execute and affect other module IRQs.
This means, in terms of execution time, ufshcd_threaded_intr
could be longer than ufshcd_intr. But if ufshcd_intr calls 
ufshcd_threaded_intr, then the execution time of 
ufshcd_intr becomes equal to ufshcd_threaded_intr, 
and that’s the part confuses me.

Of course, if you look deeper into ufshcd_threaded_intr,
you'll see that in MCQ mode, it doesn’t actually run for 
very long time. But compared to this patch, the readability
would be a bit worse. So I prefer this patch.

Thanks
Peter