Re: [PATCH 4/4] aio: allow direct aio poll comletions for keyed wakeups

[Christoph Hellwig]

On Mon, Aug 06, 2018 at 03:27:05PM -0700, Andrew Morton wrote:
> On Mon,  6 Aug 2018 10:30:58 +0200 Christoph Hellwig <hch@xxxxxx> wrote:
> 
> > If we get a keyed wakeup for a aio poll waitqueue and wake can acquire the
> > ctx_lock without spinning we can just complete the iocb straight from the
> > wakeup callback to avoid a context switch.
> 
> Why do we try to avoid spinning on the lock?

Because we are called with the lock on the waitqueue called, which
nests inside it.

> > +		/* try to complete the iocb inline if we can: */
> 
> ie, this comment explains 'what" but not "why".
> 
> (There's a typo in Subject:, btw)

Because it is faster obviously.  I can update the comment.