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

James Cameron quozl at laptop.org
Tue May 11 19:56:47 EDT 2010

On Tue, May 11, 2010 at 07:30:15PM -0400, John Watlington wrote:
> On May 11, 2010, at 7:24 PM, James Cameron wrote:
> > On Tue, May 11, 2010 at 07:14:53PM -0400, John Watlington wrote:
> >> Writes in UNIX are typically asynchronous --- get the data into a memory
> >> buffer and the program can continue along its merry way.
> >> I strongly suspect that writes through the SD system are forced to wait
> >> for the media to complete the write.
> > 
> > My tests show that our kernel is doing this for USB and SD, on ext2,
> > ext3, ext4, vfat, and raw access to the block device (open ... write ...
> > write ... close).  It isn't doing it for writes to tmpfs or null.
> Are sync writes forced on removable media ?

No.  Most writes pass in a time consistent with caching, and the latency
is so small that I'm certain they aren't reaching the media (60us).
It's only some writes that are delayed by 600ms to 3000ms.

James Cameron

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