#10045 HIGH 1.5-sof: XO-1.5 Record audio/video are out of sync with each other

[Martin Langhoff]

On Wed, May 12, 2010 at 1:46 AM, James Cameron <quozl at laptop.org> wrote:
> With the 250Mb test I've been doing, this causes 8 seconds in dd, 147
> seconds in sync, and a nice distribution of write latencies (largest
> samples 0.2s 0.1s 44ms 15ms 8ms, median 85us, smallest sample 80us).

Great! Must say that dirty_ratio=90 seems high -- default is 20, which
is 20% of available memory.

I think your settings look like

vm.dirty_background_ratio=10
vm.dirty_expire_centisecs=60000
vm.dirty_ratio=90
vm.dirty_writeback_centisecs=0

can you test with

vm.dirty_writeback_centisecs=100 # frequent pdflush process wakeups
vm.dirty_expire_centisecs=500 # make data qualify for pdflush earlier
vm.dirty_background_ratio=10 # pdflush should start working early
vm.dirty_ratio=30 # or maybe 40 -- this is the backstop

this should kickoff a background writer early, and make data "ripe"
for it to flush early too.

The downside here is that a low dirty_writeback_centisecs generates
kernel wakeups. Those wakeups can be liberally skipped when the system
is clearly idle -- but I doubt there is currently a dynamic test for
that...

> Oh I wish I had a storage activity LED on internal SD.  ;-)

Perhaps iotop helps without disturbing the results too much?

cheers,


m
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