MicroSD Card performance variance on XO-1.5

[Tomeu Vizoso]

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
workload.

Regards,

Tomeu

> But that's my (naive?) take. I haven't delved into the gstreamer madness.
>
>
> m
> --
>  martin.langhoff at gmail.com
>  martin at laptop.org -- School Server Architect
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