Re: [PATCH 3/3] blk-mq: Use llist_head for blk_cpu_done

On Sat, Oct 31, 2020 at 09:01:45AM -0600, Jens Axboe wrote:

On 10/31/20 9:00 AM, Jens Axboe wrote:

quoted

On 10/31/20 4:41 AM, Sebastian Andrzej Siewior wrote:

quoted

On 2020-10-29 14:07:59 [-0700], Sagi Grimberg wrote:

quoted

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in which context?

Not sure what is the question.

The question is in which context do you complete your requests. My guess
by now is "usually softirq/NAPI and context in rare error case".

There really aren't any rules for this, and it's perfectly legit to
complete from process context. Maybe you're a kthread driven driver and
that's how you handle completions. The block completion path has always
been hard IRQ safe, but possible to call from anywhere.

A more recent example is polled IO, which will always complete from
process/task context and very much is fast path.

But we never IPI for that anyway, so it is the easy case.