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

[Manfred Spraul]

Ben LaHaise wrote:
> 
> On Tue, 6 Feb 2001, Ingo Molnar wrote:
> 
> >
> > On Tue, 6 Feb 2001, Ben LaHaise wrote:
> >
> > > This small correction is the crux of the problem: if it blocks, it
> > > takes away from the ability of the process to continue doing useful
> > > work.  If it returns -EAGAIN, then that's okay, the io will be
> > > resubmitted later when other disk io has completed.  But, it should be
> > > possible to continue servicing network requests or user io while disk
> > > io is underway.
> >
> > typical blocking point is waiting for page completion, not
> > __wait_request(). But, this is really not an issue, NR_REQUESTS can be
> > increased anytime. If NR_REQUESTS is large enough then think of it as the
> > 'absolute upper limit of doing IO', and think of the blocking as 'the
> > kernel pulling the brakes'.
> 
> =)  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.
>
Has that anything to do with kiobuf or buffer head?

Several kernel functions need a "dontblock" parameter (or a callback, or
a waitqueue address, or a tq_struct pointer). 

--
        Manfred
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