a7fc4c85e3
zfs_zstd_cache_reap_now is issued every second.
zstd_mempool_reap checks for both pool existence and buffer count, but
that's still 2 func calls which are trivially avoidable.
With clang it even avoids pushing the stack pointer (but still suffers
the mispredict due to a forward jump, not modified in case someone is
using zstd):
<+0>: cmpq $0x0,0x0(%rip) # <zfs_zstd_cache_reap_now+8>
<+8>: je 0x217de4 <zfs_zstd_cache_reap_now+36>
<+10>: push %rbp
<+11>: mov %rsp,%rbp
<+14>: mov 0x0(%rip),%rdi # <zfs_zstd_cache_reap_now+21>
<+21>: call 0x217df0 <zstd_mempool_reap>
<+26>: mov 0x0(%rip),%rdi # <zfs_zstd_cache_reap_now+33>
<+33>: pop %rbp
<+34>: jmp 0x217df0 <zstd_mempool_reap>
<+36>: ret
Preferably the call would not be made to begin with if zstd is not used,
but this retains all the logic confined to zstd code.
Sponsored by: Rubicon Communications, LLC ("Netgate")
Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>
Reviewed-by: Allan Jude <allan@klarasystems.com>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
|
||
|---|---|---|
| .. | ||
| include | ||
| lib | ||
| README.md | ||
| zfs_zstd.c | ||
| zstd-in.c | ||
| zstd_sparc.c | ||
README.md
ZSTD-On-ZFS Library Manual
Introduction
This subtree contains the ZSTD library used in ZFS. It is heavily cut-down by dropping any unneeded files, and combined into a single file, but otherwise is intentionally unmodified. Please do not alter the file containing the zstd library, besides upgrading to a newer ZSTD release.
Tree structure:
zfs_zstd.care the actualzfskernel module hooks.lib/contains the unmodified version of theZstandardlibraryzstd-in.cis our template file for generating the single-file libraryinclude/: This directory contains supplemental includes for platform compatibility, which are not expected to be used by ZFS elsewhere in the future. Thus we keep them private to ZSTD.
Updating ZSTD
To update ZSTD the following steps need to be taken:
- Grab the latest release of ZSTD.
- Copy the files output by the following script to
module/zstd/lib/:grep include [path to zstd]/contrib/single_file_libs/zstd-in.c | awk '{ print $2 }' - Remove debug.c, threading.c, and zstdmt_compress.c.
- Update Makefiles with resulting file lists.
- Follow symbol renaming notes in
include/zstd_compat_wrapper.h
Altering ZSTD and breaking changes
If ZSTD made changes that break compatibility or you need to make breaking changes to the way we handle ZSTD, it is required to maintain backwards compatibility.
We already save the ZSTD version number within the block header to be used to add future compatibility checks and/or fixes. However, currently it is not actually used in such a way.