On Thu, 14 Apr 2016, Matthew Giassa wrote: > Hi Alan, > > You are correct: the software claims and releases certain interfaces > frequently. How frequently? The usbmon log you attached to the Bugzilla report shows it happening at intervals of approximately 20-40 ms (sometimes longer) -- and often with no messages sent in between. Does that seem at all reasonable? > The cameras have one interface with a single BULK IN endpoint, which is > used to request image data from the camera via asynchronous bulk reads > via libusb. The interface is claimed for the duration of media > streaming, and is released when streaming concludes (usually from the > user issuing a "Stop Streaming" command via the API I maintain). > > The cameras have a second interface with a BULK IN and BULK OUT endpoint > which is used to read/write internal registers on the camera (set frame > rate, on-chip processing options, etc). One of my requirements is that > that camera allows multiple processes to potentially control it, but > only one processes to actually grab the streaming data from it. > > To accomplish this, each camera has a boost::named_mutex (ie: > multi-process capable mutex) to lock down access to the control > interface. When any process wants to issue a control request to that > camera, it has to: > 1. Lock the named mutex. > 2. Claim the interface. > 3. Issue the synchronous r/w call it wants. > 4. Release the interface. > 5. Unlock the mutex. Then why does the log show sequences of claim/release with no synchronous r/w call in between? > I put the mutex in in place as I was not certain if libusb enforces > serialization of synchronous r/w requests to the same interface, and the > claim/release calls are required, to my understanding; before I do > anything with an interface. > > With LPM enabled, r/w calls to the "control" interface are much slower, > and read calls to the "streaming" interface are very slow (maybe one > frame per minute, if it doesn't seize up entirely). Have you tried, just for the sake of testing, getting rid of all those claims and releases? Simply claim both interfaces once, at the start of the program, and release them at the end. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
