Date: Sun, 23 Jan 2011 10:45:35 +1030 From: "Daniel O'Connor" <doconnor@gsoft.com.au> To: Hans Petter Selasky <hselasky@c2i.net> Cc: freebsd-usb@freebsd.org Subject: Re: libusb performance on 8.1 Message-ID: <6B2C00E3-1BDB-48D5-AC3E-E2ED7091E194@gsoft.com.au> In-Reply-To: <201101221433.23194.hselasky@c2i.net> References: <9CF6C32F-E230-446B-94FC-C57F0F02B0E4@gsoft.com.au> <201101221433.23194.hselasky@c2i.net>
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On 23/01/2011, at 24:03, Hans Petter Selasky wrote: >> While doing some speed testing I find that FreeBSD does ~4Mb/sec, but Linux >> does 17Mb/sec & OS X does 8-10Mb/sec. > > You need to change the way you buffer the data. FreeBSD does not queue more > than 2 URB's at any time, and the turnaround time varies from 1ms to 125us due > to hardware IRQ restrictions. Linux queues up all it can get, which leads to > other kind of problems. The current internal buffer limit is 16Kbyte 8000 > times per second which gives a MAX of 128 MByte/second. > > In general during hardware design: > > 1) Avoid short packets. > 2) Make sure transfer buffers are matched between host and device. > > From my experience it is very possible to reach +30Mbyte/second with LibUSB > under FreeBSD 8.2+, given the buffering is optimal for the kernel. > Hmm... I am transferring fixed size packets of 512 bytes, so there shouldn't be any short packets (unless I misunderstand what you mean). Ahh, I I see what you mean now.. I was transferring a single packet at a time because I didn't realise you could transfer more at once. If I switch to transferring 2k at once it goes up to 16Mb/sec. Thanks :) -- Daniel O'Connor software and network engineer for Genesis Software - http://www.gsoft.com.au "The nice thing about standards is that there are so many of them to choose from." -- Andrew Tanenbaum GPG Fingerprint - 5596 B766 97C0 0E94 4347 295E E593 DC20 7B3F CE8C
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