Hi list,
Le 29/04/2021 à 15:31, Nick Terrell a écrit :
From: Nick Terrell <terrelln@xxxxxx>
Please pull from
git@xxxxxxxxxx:terrelln/linux.git tags/v11-zstd-1.4.10
to get these changes. Alternatively the patchset is included.
This patchset lists me as the maintainer for zstd and upgrades the zstd library
to the latest upstream release. The current zstd version in the kernel is a
modified version of upstream zstd-1.3.1. At the time it was integrated, zstd
wasn't ready to be used in the kernel as-is. But, it is now possible to use
upstream zstd directly in the kernel.
I have not yet released zstd-1.4.10 upstream. I want the zstd version in the
kernel to match up with a known upstream release, so we know exactly what code
is running. Whenever this patchset is ready for merge, I will cut a release at
the upstream commit that gets merged. This should not be necessary for future
releases.
The kernel zstd library is automatically generated from upstream zstd. A script
makes the necessary changes and imports it into the kernel. The changes are:
1. Replace all libc dependencies with kernel replacements and rewrite includes.
2. Remove unncessary portability macros like: #if defined(_MSC_VER).
3. Use the kernel xxhash instead of bundling it.
This automation gets tested every commit by upstream's continuous integration.
When we cut a new zstd release, we will submit a patch to the kernel to update
the zstd version in the kernel.
I've updated zstd to upstream with one big patch because every commit must build,
so that precludes partial updates. Since the commit is 100% generated, I hope the
review burden is lightened. I considered replaying upstream commits, but that is
not possible because there have been ~3500 upstream commits since the last zstd
import, and the commits don't all build individually. The bulk update preserves
bisectablity because bugs can be bisected to the zstd version update. At that
point the update can be reverted, and we can work with upstream to find and fix
the bug. After this big switch in how the kernel consumes zstd, future patches
will be smaller, because they will only have one upstream release worth of
changes each.
This patchset adds a new kernel-style wrapper around zstd. This wrapper API is
functionally equivalent to the subset of the current zstd API that is currently
used. The wrapper API changes to be kernel style so that the symbols don't
collide with zstd's symbols. The update to zstd-1.4.6 maintains the same API
and preserves the semantics, so that none of the callers need to be updated.
This patchset comes in 2 parts:
1. The first 2 patches prepare for the zstd upgrade. The first patch adds the
new kernel style API so zstd can be upgraded without modifying any callers.
The second patch adds an indirection for the lib/decompress_unzstd.c
including of all decompression source files.
2. Import zstd-1.4.10. This patch is completely generated from upstream using
automated tooling.
I tested every caller of zstd on x86_64. I tested both after the 1.4.10 upgrade
using the compatibility wrapper, and after the final patch in this series.
I tested kernel and initramfs decompression in i386 and arm.
I ran benchmarks to compare the current zstd in the kernel with zstd-1.4.6.
I benchmarked on x86_64 using QEMU with KVM enabled on an Intel i9-9900k.
I found:
* BtrFS zstd compression at levels 1 and 3 is 5% faster
* BtrFS zstd decompression+read is 15% faster
* SquashFS zstd decompression+read is 15% faster
* F2FS zstd compression+write at level 3 is 8% faster
* F2FS zstd decompression+read is 20% faster
* ZRAM decompression+read is 30% faster
* Kernel zstd decompression is 35% faster
* Initramfs zstd decompression+build is 5% faster
The latest zstd also offers bug fixes. For example the problem with large kernel
decompression has been fixed upstream for over 2 years
https://lkml.org/lkml/2020/9/29/27.
Please let me know if there is anything that I can do to ease the way for these
patches. I think it is important because it gets large performance improvements,
contains bug fixes, and is switching to a more maintainable model of consuming
upstream zstd directly, making it easy to keep up to date.
Best,
Nick Terrell
I've been using this series on stable kernel since 5.12.3 (now on
5.12.10) on my main system without issues.
Tested-by: Jean-Denis Girard <jd.girard@xxxxxxxxx>
Thanks,
--
Jean-Denis Girard
SysNux Systèmes Linux en Polynésie française
https://www.sysnux.pf/ Tél: +689 40.50.10.40 / GSM: +689 87.797.527
