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On 5/24/2021 1:10 PM, Bart Van Assche wrote:

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On 5/24/21 1:36 AM, Can Guo wrote:

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Current UFS IRQ handler is completely wrapped by host lock, and

because

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ufshcd_send_command() is also protected by host lock, when IRQ

handler

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fires, not only the CPU running the IRQ handler cannot send new

requests,

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the rest CPUs can neither. Move the host lock wrapping the IRQ handler

into

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specific branches, i.e., ufshcd_uic_cmd_compl(), ufshcd_check_errors(),
ufshcd_tmc_handler() and ufshcd_transfer_req_compl(). Meanwhile, to

further

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reduce occpuation of host lock in ufshcd_transfer_req_compl(), host

lock

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is

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no longer required to call __ufshcd_transfer_req_compl(). As per test,

the

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optimization can bring considerable gain to random read/write

performance.

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An additional question is whether it is necessary for v3.0 UFS devices
to serialize the submission path against the completion path? Multiple
high-performance SCSI LLDs support hardware with separate submission

and

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completion queues and hence do not need any serialization between the
submission and the completion path. I'm asking this because it is likely
that sooner or later multiqueue support will be added in the UFS
specification. Benefiting from multiqueue support will require to rework
locking in the UFS driver anyway.

Hi Bart,
No it's not necessary to serialize both the paths. I think this series
attempts to remove this serialization to a certain degree, which is
what's giving the performance improvement.

Btw, Is this performance improvement is on top of rq_affinity 2 or 1?

Thanks,
Avri

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Even if multiqueue support would be available in the future, I think
this change is apt now for the current available specification.

I agree - this looks like the harbinger of a major change,
And going further with respect of hw queues,
will need the spec support - e.g. doorbell per lane, etc.

Thanks,
Avri

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Thanks,

Bart.

Thanks,
-asd

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