On 04/02/2011 03:56, Daniel O'Connor wrote:
I hooked up a logic analyser and I can see most of the time it's fairly
regularly transferring 16k of data every 2msec.
If I load up the disk by, eg, tar -cf /dev/null /local0 I find it drops out and
I can see gaps in the transfers until eventually the FIFO fills up and it stops.
I am wondering if this is a scheduler problem (or I am expecting too much :) in
that it is not running my libusb thread reliably under load. The other
possibility is that it is a USB issue, although I am looking at using
isochronous transfers instead of bulk.
I'm surprised this isn't complained about more often - I also regularly
see that file system activity blocks other, non-file-using processes
which are mostly CPU and memory intensive (but since I'm not running
realtime things, it fell under the "good enough" category). Maybe there
is kind of global-ish lock of some kind which the VM or the VFS hold
which would interfere with normal operation of other processes (maybe
when the processes use malloc() to grow their memory?).
Could you try 2 things:
1) instead of doing file IO, could you directly use a disk device (e.g.
/dev/ad0), possibly with some more intensive utility than dd (e.g.
"diskinfo -vt") and see if there is any difference?
2) if there is a difference in 1), try modifying your program to not
use malloc() in the critical path (if applicable) and/or use mlock(2)?
_______________________________________________
freebsd-hackers@freebsd.org mailing list
http://lists.freebsd.org/mailman/listinfo/freebsd-hackers
To unsubscribe, send any mail to "freebsd-hackers-unsubscr...@freebsd.org"
