Re: Updated bootchart (rev1543)

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Alkis Georgopoulos wrote:
> Since the nbd image is read-only, can't we tell the kernel to cache
> every block that it reads from it, so that it only needs to read each
> block once, if the RAM suffices?

It's already doing caching, actually, I find 20s for a full boot
perfectly acceptable especially as I think we'll easily get that down to
15s or even faster depending on the work Ubuntu's doing.

Just for the record, currently on the same hardware with a SSD, it takes
19s to boot, so LTSP is perfectly on track there.

> 
> If the kernel already does that automatically, maybe *somehow* enabling
> readahead would help? Or maybe a bigger block size?

Well, that won't really work, I did some tests with ureadahead and it's
quite linked with the hardware + you need to boot a thin client to get
the binary file to include on your chroot, so that can't be scripted as
part of ltsp-build-client.

> 
> 
> Btw, I'd be interested to see how nbd-proxy affects low-end client
> performance, e.g. PIII / 64 RAM. Stéphane, when the optimizations are
> done, could you please notify me to do some testing?

Sure, I'll poke you. nbd-proxy shouldn't add much overhead other than
having data moving a lot between kernel and userspace. Currently
something must be wrong in the code as it's not killing the CPU and
gives us poor performance, must be a simple bug somewhere.

> 
> -Alkis


- --
Stéphane Graber
Ubuntu developer
http://www.ubuntu.com
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