Re: [RFC][PATCH 1/3] sched, block: Move unplug

[Jens Axboe <jaxboe@fusionio.com>]

On 2011-06-22 01:34, Peter Zijlstra wrote:
> Thomas found that we're doing a horrendous amount of work in that scheduler
> unplug hook while having preempt and IRQs disabled.
> 
> Move it to the head of schedule() where both preemption and IRQs are enabled
> such that we don't get these silly long IRQ/preempt disable times.
> 
> This allows us to remove a lot of special magic in the unplug path,
> simplifying that code as a bonus.

The major change here is moving the queue running inline, instead of
punting to a thread. The worry is/was that we risk blowing the stack if
something ends up blocking inadvertently further down the call path.
Since it's the unlikely way to unplug, a bit of latency was acceptable
to prevent this problem.

I'm curious why you made that change? It seems orthogonal to the change
you are actually describing in the commit message.

-- 
Jens Axboe