Red Hat Bugzilla – Bug 64404
increased latency causes drops in video capture
Last modified: 2015-01-04 17:01:44 EST
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Description of problem:
I use avifile to divx capture tv to disk at email@example.com. Under
2.4.9-31 & 2.4.3 I can capture/compress without frame drops, but under
kernel-2.4.18-22 & 26 I get 2-3% frame drops which seem to be tied to
disk flushing activity.
Version-Release number of selected component (if applicable):
Steps to Reproduce:
1.grab athlon with scsi disk subsystem (u2w striped)
3.capture 5minutes at firstname.lastname@example.org fps divx4 (low-motion)
4.review frame drops
Actual Results: Under 2.4.9 I get less that 1% (13 out of 4200 frames captured)
Under 2.4.18 I get about 2-3% drops in bursts clustered arround scsi-disk io.
By contrast my 2.4.3 kernel system (K7-800 ide disk) drops 4 frames in a hour.
As near as I can tell, this tied to the new VM subsystem, based on
the frame drops not occuring under prior kernel releases
(I used 2.2.19 & 2.4.3 also with no frame drops). So despite Morton's
low-latency patch in 2.4.18-22/26, there appears to be issues still
with the VM subsystem flushing buffers to disk. I can aggravate the
issue by adjusting the bdflush parameters, but can't prevent it.