Messages in this thread |  | | | Subject | Re: Problem with read blocking for a long time on /dev/scd1 | | From | Greg Stark <> | | Date | 21 Dec 2002 01:14:38 -0500 |
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Gregory Stark <gsstark@MIT.EDU> writes:
> I'm having a problem with ogle that seems to be being caused by the scsi or > ide-scsi driver. The video playback freezes for a second or randomly, > sometimes every few seconds, sometimes not for several minutes. Every such > glitch is correlated perfectly with a read syscall reading on /dev/scd1 > blocking for an inordinate amount of time. > > Most read syscalls from ogle seem to take between 30us to 100ms depending on > the size of the read. In fact plotting the time taken reported by strace -T vs > the size of the read in gnuplot produces a nice obvious linear correlation.
One more piece of data I just found. Whenever the read blocks for a long time like this it seems ps lists the process's wait channel as "lock_p". The only matching symbol is lock_page.
Does that help narrow down the source of the latency or is that just what the device driver happens to use as its synchronization primitive?
-- greg
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