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Subject: [PATCH 0/6] lib/lzo: performance improvements
Thread-Topic: [PATCH 0/6] lib/lzo: performance improvements
Thread-Index: AQHUgZI88EDtuaHmFU63dmJG+DkKOw==
Date:   Wed, 21 Nov 2018 12:06:02 +0000
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This patch series introduces performance improvements for lzo.

The improvements fall into two categories: general Arm-specific optimisatio=
ns
(e.g., more efficient memory access); and the introduction of a special cas=
e=A0
for handling runs of zeros (which is a common case for zram) using run-leng=
th
encoding.

The introduction of RLE modifies the bitstream such that it can't be decode=
d
by old versions of lzo (the new lzo-rle can correctly decode old bitstreams=
).
To avoid possible issues where data is persisted on disk (e.g., squashfs), =
the=A0
final patch in this series separates lzo-rle into a separate algorithm
alongside lzo, so that the new lzo-rle is (by default) only used for zram a=
nd
must be explicitly selected for other use-cases. This final patch could be
omitted if the consensus is that we'd rather avoid proliferation of lzo
variants.

Overall, performance is improved by around 1.1 - 4.8x (data-dependent: data
with many zero runs shows higher improvement). Under real-world testing wit=
h
zram, time spent in (de)compression during swapping is reduced by around 27=
%.
The graph below shows the weighted round-trip throughput of lzo, lz4 and
lzo-rle, for randomly generated 4k chunks of data with varying levels of
entropy. (To calculate weighted round-trip throughput, compression performa=
nce
is emphasised to reflect the fact that zram does around 2.25x more compress=
ion
than decompression. (Results and overall trends are fairly similar for
unweighted).

https://drive.google.com/file/d/18GU4pgRVCLNN7wXxynz-8R2ygrY2IdyE/view

Contributors:
Dave Rodgman <dave.rodgman@arm.com>
Matt Sealey <matt.sealey@arm.com>=