Messages in this thread |  | | | From | Oliver Neukum <> | | Subject | Re: [PATCH 5/5] usb_debug: EXPERIMENTAL - poll hcd device to force writes | | Date | Thu, 7 May 2009 17:01:50 +0200 |
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Am Donnerstag, 7. Mai 2009 16:35:57 schrieb Alan Stern: > 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.
This is true only if the device's buffer would run dry. But if no URB is in flight, a URB should be written right away.
> 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).
Hm, you say many URBs can complete before an interrupt handler can react?
Regards Oliver
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