Re: [edk2-devel] Multithreaded compression with LZMA2

["Laszlo Ersek" <lersek@redhat.com>]

On 12/02/20 03:59, Daniel Schaefer wrote:
> Hi everyone,
> 
> I'm looking into how to speed up the build process and noticed that our
> build
> uses LZMA to encrypt the main firmware volume. Since it's quite big it
> takes a
> while but only uses one CPU thread.
> 
> LZMA2 is a version of LZMA which can be multi-threaded and achieve much
> faster
> compression times. I did a quick benchmark using the `xz` command-line
> tool,
> which uses a modified version of the LZMA SDK that EDK2 uses. The
> results are:
> 
> Uncompressed size: 64M
> 
> | Algo  | Comp Time | Decomp Time | Size | Threads |
> | ----- | --------- | ----------- | ---- | ------- |
> | LZMA  |    19.67s |        0.9s | 9.1M |       1 |
> | LZMA2 |    20.11s |        1.2s | 9.2M |       1 |
> | LZMA2 |     8.31s |        1.0s | 9.4M |       4 |
> 
> Using those commands:
> 
> time xz --format=lzma testfile
> time unlzma testfile.lzma
> 
> time xz --lzma2 testfile
> time unxz testfile.xz
> 
> time xz -T4 --lzma2 testfile
> time unxz testfile.xz
> 
> This is quite a significant improvement of build time, while
> decompression time
> and size only slightly increase. If that's a concern, then LZMA2 could
> be used
> for development only.
> 
> I haven't investigated the details of how to support this in the code
> but it
> appears to be a simple change, since the LZMA SDK that we use already
> supports
> LZMA2.
> 
> What do you think?

"xz -T" works by splitting the input into blocks, and it generates a
multi-block compressed output. I'm unsure if the current LZMA
decompressor that runs inside the firmware (= guided section extractor)
copes with multi-block input.

Thanks
Laszlo