Patrick Steinhardt <ps@xxxxxx> writes: > Hi, > > I have recently started to play around with zlib-ng a bit, which is a > hard fork of the zlib library. It describes itself as zlib replacement > with optimizations for "next generation" systems. As such, it contains > several implementations of central algorithms using for example SSE2, > AVX2 and other vectorized CPU intrinsics that supposedly speed up in- > and deflating data. > > And indeed, compiling Git against zlib-ng leads to a significant speedup > when reading objects. The following benchmark uses git-cat-file(1) with > `--batch --batch-all-objects` in the Git repository: > > Benchmark 1: zlib > Time (mean ± σ): 52.085 s ± 0.141 s [User: 51.500 s, System: 0.456 s] > Range (min … max): 52.004 s … 52.335 s 5 runs > > Benchmark 2: zlib-ng > Time (mean ± σ): 40.324 s ± 0.134 s [User: 39.731 s, System: 0.490 s] > Range (min … max): 40.135 s … 40.484 s 5 runs > > Summary > zlib-ng ran > 1.29 ± 0.01 times faster than zlib > > So we're looking at a ~25% speedup compared to zlib. This is of course > an extreme example, as it makes us read through all objects in the > repository. But regardless, it should be possible to see some sort of > speedup in most commands that end up accessing the object database. > > This patch series refactors how we wire up zlib in our project by > introducing a new "compat/zlib.h" header function. This header is then > later extended to patch over the differences between zlib and zlib-ng, > which is mostly just that zlib-ng has a `zng_` prefix for each of its > symbols. Like this, we can support both libraries directly, and a new > Meson build options allows users to pick whichever backend they like. > > In theory, these changes shouldn't be necessary because zlib-ng provides > a compatibility layer that make it directly compatible with zlib. But > most distros don't allow you to install zlib-ng with that layer is it > would mean that zlib would need to be replaced globally. Instead, they > typically only provide a version of zlib-ng that only has the `zng_` > prefixed symbols. > > Given the observed speedup I do think that this is a worthwhile change > so that users (or especially hosting providers) can easily switch to > zlib-ng without impacting the rest of their system. > > Changes in v2: > - Wire up zlib-ng in our Makefile. > - Exercise zlib-ng via CI by adapting our "linux-musl" job to use > Meson and installing zlib-ng. > - Link to v1: https://lore.kernel.org/r/20250110-b4-pks-compat-drop-uncompress2-v1-0-965d0022a74d@xxxxxx > Apart from a few typos, Patrick has already answered two of questions and the series already looks good to me! Thanks [snip]
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