Re: [Kiobuf-io-devel] RFC: Kernel mechanism: Compound event wait

[Manfred Spraul]

Linus Torvalds wrote:
> 
> On Tue, 6 Feb 2001, Manfred Spraul wrote:
> > Jens Axboe wrote:
> > >
> > > > Several kernel functions need a "dontblock" parameter (or a callback, or
> > > > a waitqueue address, or a tq_struct pointer).
> > >
> > > We don't even need that, non-blocking is implicitly applied with READA.
> > >
> > READA just returns - I doubt that the aio functions should poll until
> > there are free entries in the request queue.
> 
> The aio functions should NOT use READA/WRITEA. They should just use the
> normal operations, waiting for requests.

But then you end with lots of threads blocking in get_request()

Quoting Ben's mail:
<<<<<<<<<
> 
> =)  This is what I'm seeing: lots of processes waiting with wchan ==
> __get_request_wait.  With async io and a database flushing lots of io
> asynchronously spread out across the disk, the NR_REQUESTS limit is hit
> very quickly.
> 
>>>>>>>>>

On an io bound server the request queue is always full - waiting for the
next request might take longer than the actual io.

--
        Manfred
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