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SubjectRe: [RFC PATCH 0/6] Convert all tasklets to workqueues

* Christoph Hellwig <hch@infradead.org> wrote:

> Note that we also have a lot of inefficiency in the way we do deferred
> processing. Think of a setup where you run a XFS filesystem runs over
> a megaraid adapter.
>
> (1) we get a real hardirq, which just clears the interrupt and then
> deferes to a tasklet
> (2) tasklet walks the producer / consumer queue and then calls scsi_done
> for each completeted scsi command which ends up doing
> raise_softirq_irqoff(BLOCK_SOFTIRQ);
> (3) block softirq does the heavy lifting for command completion and finally
> calls back into the bio's completion routine
> (4) xfs wants to avoid irq safe locking and thus deferes the command to a
> kthread

i dont understand - why is a tasklet used at all? Why not do it straight
in the BLOCK_SOFTIRQ? Using tasklets there is extra, unnecessary
overhead already.

Ingo
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