Re: [PATCH 3/3 v2] blk-mq: Use llist_head for blk_cpu_done

[Daniel Wagner]

On Mon, Jan 25, 2021 at 10:54:12AM +0100, Sebastian Andrzej Siewior wrote:
> With llist_head it is possible to avoid the locking (the irq-off region)
> when items are added. This makes it possible to add items on a remote
> CPU without additional locking.
> llist_add() returns true if the list was previously empty. This can be
> used to invoke the SMP function call / raise sofirq only if the first
> item was added (otherwise it is already pending).
> This simplifies the code a little and reduces the IRQ-off regions.
> 
> blk_mq_raise_softirq() needs a preempt-disable section to ensure the
> request is enqueued on the same CPU as the softirq is raised.
> Some callers (USB-storage) invoke this path in preemptible context.
> 
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>

I did a quick test run with the whole series. Looks good.

Reviewed-by: Daniel Wagner <dwagner@xxxxxxx>