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

[James Cameron]

On Tue, May 11, 2010 at 11:29:08PM -0400, John Watlington wrote:
> Reading the patch, it sounds like a better set of parameters
> to try would be:
> vm.dirty_background_ratio=10
> vm.dirty_bytes=90

dirty_bytes of 90 is rounded down to nearest page size; in this case
zero.  Instead, I suspect you mean:

vm.dirty_background_ratio=10
vm.dirty_ratio=90

Which means that as a process writes, it will not suffer any impact
until 10% of memory is filled with dirty buffers, then it will suffer
pdflush contention, and then when 90% of memory is filled with dirty
buffers it will face delays as writes will start writeback.

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).

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

-- 
James Cameron
http://quozl.linux.org.au/