Re: [PATCH 1/3] Separate IRQ-stacks from 4K-stacks option

[Arjan van de Ven]

On Mon, Sep 13, 2004 at 12:31:58PM +0200, Andrea Arcangeli wrote:
> On Mon, Sep 13, 2004 at 09:32:59AM +0200, Jens Axboe wrote:
> > completion from hardirq context, SCSI is the exception since it does it
> > defers the completion to softirq context.
> 
> which btw doesn't really make much difference at all to run it in irq
> context with irq enabled since it'll run from irq context anyways and
> you'll still depend on nested hardirqs to avoid huge latencies from
> softirq handlers (the most difference between softirq and hardirq with
> irq enabled happens if you can use spin_lock_bh instead of spin_lock_irq
> in the critical sections to protect against other cpus).

and there is improved batching under really high (irq) load, esp when you
deal with stupid hw that can't give an irq for multiple packets or IO
requests at the same time (qlogic used to be like that until the driver got
fixed)

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