Date: Sat, 29 Nov 2008 00:31:22 +0100 From: Thierry Herbelot <thierry.herbelot@free.fr> To: Hans Petter Selasky <hselasky@c2i.net> Cc: freebsd-usb@freebsd.org Subject: Re: usb2 bulk read optimization ? Message-ID: <200811290031.22513.thierry.herbelot@free.fr> In-Reply-To: <200811281906.00913.hselasky@c2i.net> References: <200811281606.51927.thierry.herbelot@free.fr> <200811281906.00913.hselasky@c2i.net>
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Le Friday 28 November 2008, Hans Petter Selasky a écrit : > On Friday 28 November 2008, Thierry Herbelot wrote: > > Hello, > > > > another day, another question : > > > > I'm done converting an old "userland driver" to usb2 and libusb20 - and > > it works ! (using the libusb API, for the time being). > > > > The application is a data capture from a bulk endpoint, and I can't get > > more than around 8 Mbps. The data are formatted as URBs of 40 kbytes. > > > > This may be expected, as the machine is an oldish Pentium-III, with an > > additional Acer-based USB-2 extension card. > > > > (still, I have recompiled the -current kernel without the INVARIANTS and > > WITNESS options) > > > > I have had a quick look at the code of libusb20 and tried an increase of > > bufsize in usb_get_transfer_by_ep_no, but with no discernable > > improvements. > > > > Any idea ? > > Hi Thierry, > > You have found the correct place to tune the buffer size. Are you sure that > your application is also doing similiarly large bulk transfers? I'm doing "usb_bulk_read(handle, ep, data, size, 500);" with size around 40kbytes. > > Are you sure that the transfer speed limitation is not a limitation of your > USB device? this USB device is known, with a different, open-source, OS, to handle around 240Mbps (30Mbyte/s, but probably not on this oldish machine). the device is high-speed compliant, but can only do bulk transfers (maybe isochronous could have been better, but that's technically not possible) > > Keep in mind: The EHCI has an interrupt clamp of 4000-8000 interrupts / > second. OK : I would *very much* like to see a transfer rate of 4k*40kbyte/sec > > --HPS Thanks for the answers TfH
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