linux-kernel - Re: [PATCH 5/5] usb_debug: EXPERIMENTAL

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Date:	Thu, 7 May 2009 00:24:16 +0200
From:	Oliver Neukum <oliver@...kum.org>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Jason Wessel <jason.wessel@...driver.com>, greg@...ah.com,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/5] usb_debug: EXPERIMENTAL - poll hcd device to force writes

Am Mittwoch, 6. Mai 2009 22:24:13 schrieb Alan Stern:
> On Wed, 6 May 2009, Oliver Neukum wrote:
> > Am Mittwoch, 6. Mai 2009 21:24:56 schrieb Alan Stern:
> > > On Wed, 6 May 2009, Oliver Neukum wrote:
> > >
> > > A little thought yielded the following algorithm.  It assumes there is
> > > a fixed set of URBs allocated, unlike what you have done.  Does it make
> >
> > No, it does not ;-) Your approach is more general than you think.
> > The only important constraint is that the number of URBs in flight
> > be limited. It doesn't matter when they are allocated.
>
> You're optimistically assuming that URB allocations will succeed.  I
> guess that's okay -- dropping characters when there's insufficient
> memory seems like a good thing to do.

I also have to assume submission works.

> What's the point of that "reserve_buffer" thing?  Why not just use the
> next URB's transfer buffer?

I am toying with the idea of reusing the last URB.

On a fundamental note, thinking about this in terms of numbers of URBs
is strictly speaking wrong. We need to limit data in flight. For efficiency
we should make buffers as large as possible within that limit.

	Regards
		Oliver

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