Date: Wed, 4 Mar 2009 08:33:43 -0800 From: Andrew Thompson <thompsa@FreeBSD.org> To: Hans Petter Selasky <hselasky@c2i.net> Cc: freebsd-usb@freebsd.org Subject: Re: Low perfomance when read from usb flash drive Message-ID: <20090304163343.GD17847@citylink.fud.org.nz> In-Reply-To: <200903041001.37376.hselasky@c2i.net> References: <200903032243.31914.hselasky@c2i.net> <200903040922.48163.hselasky@c2i.net> <20090304.014655.1820405796.imp@bsdimp.com> <200903041001.37376.hselasky@c2i.net>
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On Wed, Mar 04, 2009 at 10:01:36AM +0100, Hans Petter Selasky wrote: > On Wednesday 04 March 2009, M. Warner Losh wrote: > > In message: <200903040922.48163.hselasky@c2i.net> > > > > : > I am looking at using FreeBSD in an embedded product. I have not > > : > examined your ehci software, but I am aware of how Linux and other > > : > OSes run the controller. > > : > > > : > Why are you taking an interrupt every uFrame SOF? > > : > > : If the transaction completes before 125us we take the interrupt before > > : 125us. The problem is that the interrupt delay becomes critical to > > : performance when the interrupt rate is close to the interrupt limitation. > > : > > : For example: > > : > > : Transferring 13Mbyte/sec at blocksize equal to 65536 bytes generates 600 > > : interrupts. Hence the Mass Storage state machine has three steps the > > : throughput is computed like (600/3)*65536 bytes. If we on the average > > : have to wait 0.5ms for an interrupt we loose throughput. > > > > Shouldn't you be using filters and such to make this less relevant? A > > filter runs on the order of 5us after the interrupt on fast machines, > > and 20us on slower (400MHz) ones. You can feed the pipeline better, > > and handle higher interrupt rates... > > > > Yes, that's one possibility. It looks like there is some timing slightly out > of sync. I have an AMD box with the same symptoms. I will try to figure out > what is causing it. If you do change to filters then this is much easier with taskqueues as it has a fast variant, otherwise you would need an intermediate step in order to signal the existing usb threading scheme. The taskqueue changeover will be happening soonish anyway. Andrew
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