Messages in this thread | | | Date | Thu, 7 May 2009 10:35:57 -0400 (EDT) | From | Alan Stern <> | Subject | Re: [PATCH 5/5] usb_debug: EXPERIMENTAL - poll hcd device to force writes |
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On Thu, 7 May 2009, Oliver Neukum wrote:
> 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.
But for latency you should submit URBs as soone as possible within that limit, which generally means small buffers.
How about setting the upper limit to URBs in flight based on the baud rate? Faster transfers deserve more URBs, right? Assuming some minimum number of bytes per URB (4? 8?), there should be enough URBs to fill a pipeline whose length is around 5 ms or so (interrupt latency).
Alan Stern
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