MicroSD Card performance variance on XO-1.5
tomeu at sugarlabs.org
Fri Aug 6 12:50:59 EDT 2010
On Fri, Aug 6, 2010 at 18:43, Martin Langhoff <martin.langhoff at gmail.com> wrote:
> On Fri, Aug 6, 2010 at 12:30 PM, Richard A. Smith <richard at laptop.org> wrote:
>> Whats the qualifications on that? I assume its raw RGB video?
> No, it's compressed vid + uncompressed audio to be stitched later.
> I have a confession to make: Many years ago I worked in video mixing
> with mid-range gear (avid and media100, I *don't* miss you) and with
> cheapskates PC-based rigs (which where hell on wheels compared to avid
> and media100).
> My take is that our CPU is perfectly capable of capturing and
> compressing vid and audio and putting it down to disk, even on a
> 2MB/s-capable disk, helped a bit by (limited) linux kernel buffering.
> Most importantly, we need to capture audio + vid together, or at least
> timestamp them together. Otherwise drift is inevitable.
> I also think our vm.dirty_* settings are wrong and likely causing our
> current fill-buffer-and-stutter behaviour. We are using the defaults
> and those are for spinning harddrives, with a significant cost to
> spinning up the disk on a laptop -- hence long expire_centisecs and
> writeback_centisecs and the assumption that once you've started
> writing, it'll be written out fast. We have zero seek costs, zero
> "spin disk up" costs, but slowish writes -- we have to start writing
> buffers out ASAP.
I had also had the impression for some time that some knobs in the
kernel could have been better tuned for the XO-1 and the actual
> But that's my (naive?) take. I haven't delved into the gstreamer madness.
> martin.langhoff at gmail.com
> martin at laptop.org -- School Server Architect
> - ask interesting questions
> - don't get distracted with shiny stuff - working code first
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