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Qu Wenruo 9643b3baa4 btrfs: introduce btrfs_bio::async_csum 
[ Upstream commit dd57c78aec ]

[ENHANCEMENT]
Btrfs currently calculates data checksums then submits the bio.

But after commit 968f19c5b1 ("btrfs: always fallback to buffered write
if the inode requires checksum"), any writes with data checksum will
fallback to buffered IO, meaning the content will not change during
writeback.

This means we're safe to calculate the data checksum and submit the bio
in parallel, and only need the following new behavior:

- Wait the csum generation to finish before calling btrfs_bio::end_io()
  Or this can lead to use-after-free for the csum generation worker.

- Save the current bi_iter for csum_one_bio()
  As the submission part can advance btrfs_bio::bio.bi_iter, if not
  saved csum_one_bio() may got an empty bi_iter and do not generate any
  checksum.

  Unfortunately this means we have to increase the size of btrfs_bio for
  16 bytes, but this is still acceptable.

As usual, such new feature is hidden behind the experimental flag.

[THEORETIC ANALYZE]
Consider the following theoretic hardware performance, which should be
more or less close to modern mainstream hardware:

	Memory bandwidth:	50GiB/s
	CRC32C bandwidth:	45GiB/s
	SSD bandwidth:		8GiB/s

Then write bandwidth with data checksum before the patch is:

	1 / ( 1 / 50 + 1 / 45 + 1 / 8) = 5.98 GiB/s

After the patch, the bandwidth is:

	1 / ( 1 / 50 + max( 1 / 45 + 1 / 8)) = 6.90 GiB/s

The difference is 15.32% improvement.

[REAL WORLD BENCHMARK]
I'm using a Zen5 (HX 370) as the host, the VM has 4GiB memory, 10 vCPUs, the
storage is backed by a PCIe gen3 x4 NVMe.

The test is a direct IO write, with 1MiB block size, write 7GiB data
into a btrfs mount with data checksum. Thus the direct write will
fallback to buffered one:

Vanilla Datasum:	1619.97 GiB/s
Patched Datasum:	1792.26 GiB/s
Diff			+10.6 %

In my case, the bottleneck is the storage, thus the improvement is not
reaching the theoretic one, but still some observable improvement.

Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Stable-dep-of: b39b26e017 ("btrfs: zoned: don't zone append to conventional zone")
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2026-02-26 14:58:59 -08:00
arch LoongArch: Rework KASAN initialization for PTW-enabled systems 2026-02-19 16:31:34 +01:00
block block,bfq: fix aux stat accumulation destination 2026-02-11 13:41:47 +01:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto crypto: authencesn - reject too-short AAD (assoclen<8) to match ESP/ESN spec 2026-01-30 10:32:12 +01:00
Documentation fou: Don't allow 0 for FOU_ATTR_IPPROTO. 2026-01-30 10:32:12 +01:00
drivers tpm: st33zp24: Fix missing cleanup on get_burstcount() error 2026-02-26 14:58:58 -08:00
fs btrfs: introduce btrfs_bio::async_csum 2026-02-26 14:58:59 -08:00
include device_cgroup: remove branch hint after code refactor 2026-02-26 14:58:57 -08:00
init printk changes for 6.18 2025-10-04 11:13:11 -07:00
io_uring io_uring/fdinfo: be a bit nicer when looping a lot of SQEs/CQEs 2026-02-19 16:31:34 +01:00
ipc namespace-6.18-rc1 2025-09-29 11:20:29 -07:00
kernel rcu: Fix rcu_read_unlock() deadloop due to softirq 2026-02-26 14:58:57 -08:00
lib procfs: avoid fetching build ID while holding VMA lock 2026-02-11 13:41:41 +01:00
LICENSES LICENSES: Replace the obsolete address of the FSF in the GFDL-1.2 2025-07-24 11:15:39 +02:00
mm mm/hugetlb: fix excessive IPI broadcasts when unsharing PMD tables using mmu_gather 2026-02-19 16:31:34 +01:00
net ipv6: Fix ECMP sibling count mismatch when clearing RTF_ADDRCONF 2026-02-11 13:41:59 +01:00
rust rust: driver: fix broken intra-doc links to example driver types 2026-02-19 16:31:31 +01:00
samples samples/ftrace: Adjust LoongArch register restore order in direct calls 2026-01-08 10:17:11 +01:00
scripts scripts: generate_rust_analyzer: Add compiler_builtins -> core dep 2026-02-06 16:57:42 +01:00
security keys/trusted_keys: fix handle passed to tpm_buf_append_name during unseal 2026-01-30 10:32:22 +01:00
sound ASoC: fsl_xcvr: fix missing lock in fsl_xcvr_mode_put() 2026-02-19 16:31:34 +01:00
tools selftests/resctrl: Fix a division by zero error on Hygon 2026-02-26 14:58:57 -08:00
usr gen_init_cpio: Ignore fsync() returning EINVAL on pipes 2025-10-07 09:53:05 -07:00
virt KVM: Don't clobber irqfd routing type when deassigning irqfd 2026-02-11 13:41:44 +01:00
.clang-format memblock: drop for_each_free_mem_pfn_range_in_zone_from() 2025-09-14 08:49:03 +03:00
.clippy.toml rust: clean Rust 1.88.0's warning about clippy::disallowed_macros configuration 2025-05-07 00:11:47 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.editorconfig .editorconfig: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.get_maintainer.ignore MAINTAINERS: remove Alyssa Rosenzweig 2025-09-18 21:17:31 +02:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore .gitignore: ignore compile_commands.json globally 2025-08-12 15:53:55 -07:00
.mailmap 8 hotfixes. 4 are cc:stable, 7 are against mm/. 2025-11-26 12:38:05 -08:00
.pylintrc tools: docs: parse-headers.py: move it from sphinx dir 2025-08-29 15:54:42 -06:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: mark ISDN subsystem as orphan 2025-10-27 17:49:45 -07:00
Kbuild sched: Make migrate_{en,dis}able() inline 2025-09-25 09:57:16 +02:00
Kconfig io_uring: Rename KConfig to Kconfig 2025-02-19 14:53:27 -07:00
MAINTAINERS soc: fixes for 6.18, part 4 2025-11-28 09:57:31 -08:00
Makefile Linux 6.18.13 2026-02-19 16:31:37 +01:00
README README: Fix spelling 2024-03-18 03:36:32 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.