Date: Sun, 09 Aug 2009 10:23:41 -0600 (MDT) From: "M. Warner Losh" <imp@bsdimp.com> To: hps@freebsd.org Cc: usb@freebsd.org Subject: Performance issues Message-ID: <20090809.102341.2106235641.imp@bsdimp.com>
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Hans, Just trying to do some stuff I used to be able to do with the USB stack on a recent (July 23rd) kernel. I've had some disappointing results. I have a 750GB disk that's attached via USB. Nothing fancy or special about it. I can stream up to about 18MB/s to it when things are going well. Older code works flawlessly with this device. I have one other device attached, a bluetooth dongle that's really just buit into my laptop. There's no bluetooth devices attached to the laptop via this dongle, but plenty of bluetooth in the general area... The bt stack is enabled. What I see is that from time to time the writes to the disk stop for seconds at a time. This can happen when I'm writing from DV streams (which are 25Mb/s or 4.1MB/s) as well as a dd from either /dev/zero or from a dvd I have in my laptop's DVD reader. The /dev/zero ones go at about 16-18MB/s, while the DVD reader is about 5MB/s. When it happens, the process hangs in wdrain. This makes it impossible to use umass devices for things like reading my DV camera to stream things to disk for later processing into DVDs. It also seems to make it impossible to burn DVDs, since this same hic-up is seen in read speed as well. If I remove the bluetooth dongle from the system, then I don't seem to see this problem. Any ideas how to track this down? Warner
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