Date: Thu, 13 Jan 2011 22:24:54 +0100 From: Hans Petter Selasky <hselasky@c2i.net> To: freebsd-usb@freebsd.org Cc: freebsd@sopwith.solgatos.com, freebsd-firewire@freebsd.org, freebsd-questions@freebsd.org, dieterbsd@engineer.com Subject: Re: lock contention problem? Message-ID: <201101132224.54858.hselasky@c2i.net> In-Reply-To: <8CD81778A4C13E7-17B0-DFA1@web-mmc-d03.sysops.aol.com> References: <8CD81778A4C13E7-17B0-DFA1@web-mmc-d03.sysops.aol.com>
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On Thursday 13 January 2011 21:28:15 dieterbsd@engineer.com wrote:
> I suspect that I have a problem with lock/mutex contention.
> Reading from a USB disk appears to lock out the firewire driver
> for too long, causing data transfer (writing to firewire bus) to fail
> with EAGAIN. Once it fails it does not recover.
>
> kernel: fwohci1: IT DMA underrun (0x40308011) (stat &
> OHCI_CNTL_CYCMATCH_S)
> last message repeated 63 times
> This is from the end of the fwohci_itxbuf_enable() function in
> dev/firewire/fwohci.c
>
> I added LOCK_PROFILING to the kernel and gathered some data.
> The data is quite verbose, so I sorted by "max" and am including
> the first 40 lines. This is a true real-time task, so I am concerned
> with the worst case rather than the average.
>
Hi,
It might be a hardware resource starvation problem. It is possible to nice
umass by simply adding a line like:
.interval = 2, /* 2 milliseconds */
Inside the following structure in /sys/dev/usb/storage/umass.c :
umass_bbb_config[]
In states:
UMASS_T_BBB_DATA_WRITE
UMASS_T_BBB_DATA_READ
Another idea:
http://svn.freebsd.org/changeset/base/217350
--HPS
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