Re: [RFC PATCH 0/4] Add support for LZ4-compressed kernels


kyungsik.lee <kyungsik.lee@...>
 

On 2013-01-29 오후 8:43, Egon Alter wrote:
Am Dienstag, 29. Januar 2013, 10:15:49 schrieb Russell King - ARM Linux:
On Mon, Jan 28, 2013 at 02:25:10PM -0800, Andrew Morton wrote:
What's this "with enabled unaligned memory access" thing? You mean "if
the arch supports CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS"? If so,
that's only x86, which isn't really in the target market for this
patch, yes?

It's a lot of code for a 50ms boot-time improvement. Does anyone have
any opinions on whether or not the benefits are worth the cost?
Well... when I saw this my immediate reaction was "oh no, yet another
decompressor for the kernel". We have five of these things already.
Do we really need a sixth?

My feeling is that we should have:
- one decompressor which is the fastest
- one decompressor for the highest compression ratio
- one popular decompressor (eg conventional gzip)
the problem gets more complicated as the "fastest" decompressor usually
creates larger images which need more time to load from the storage, e.g. a
one MB larger image on a 10 MB/s storage (note: bootloaders often configure
the storage controllers in slow modes) gives 100 ms more boot time, thus
eating the gain of a "fast decompressor".
Yes, the larger image could matter. Definitely it takes longer.

Here are some updated test cases: Including "loading time"

lzo lz4
loading time: 480ms 510ms
decompression time: 336ms 180ms(with efficient unaligned memory access enabled and ARM optimization)
total time: 816ms 690ms

lz4 is still 15% faster in total time. This one is similar to the simulated result by Russell King.

Thanks,
Kyungsik

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