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

[Ingo Molnar]

* Christoph Hellwig <hch@xxxxxxxxxxxxx> 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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