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Qu Wenruo dd57c78aec btrfs: introduce btrfs_bio::async_csum 
[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>
2025-11-24 22:42:21 +01:00
arch Fix perf CPU-clock counters, and address a static checker warning. 2025-11-23 08:20:15 -08:00
block vfs-6.18-rc7.fixes 2025-11-17 09:11:27 -08:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto This push contains the following changes: 2025-10-10 08:56:16 -07:00
Documentation Input updates for v6.18-rc6 2025-11-22 09:58:41 -08:00
drivers Fixes for the Allwinner clk driver: 2025-11-23 12:03:28 -08:00
fs btrfs: introduce btrfs_bio::async_csum 2025-11-24 22:42:21 +01:00
include btrfs: implement shutdown ioctl 2025-11-24 21:56:17 +01:00
init printk changes for 6.18 2025-10-04 11:13:11 -07:00
io_uring io_uring/cmd_net: fix wrong argument types for skb_queue_splice() 2025-11-20 11:40:15 -07:00
ipc namespace-6.18-rc1 2025-09-29 11:20:29 -07:00
kernel Miscellaneous fixes: 2025-11-23 08:23:30 -08:00
lib Crypto library fix for v6.18-rc7 2025-11-22 11:53:53 -08:00
LICENSES LICENSES: Replace the obsolete address of the FSF in the GFDL-1.2 2025-07-24 11:15:39 +02:00
mm slab fix for 6.18-rc7 2025-11-20 10:49:12 -08:00
net Including fixes from IPsec and wireless. 2025-11-20 08:52:07 -08:00
rust rust: Add -fno-isolate-erroneous-paths-dereference to bindgen_skip_c_flags 2025-11-10 08:37:06 +08:00
samples samples: work around glibc redefining some of our defines wrong 2025-11-21 09:29:02 -08:00
scripts Rust fixes for v6.18 (2nd) 2025-11-14 15:36:15 -08:00
security selinux/stable-6.18 PR 20251121 2025-11-22 09:24:36 -08:00
sound ALSA: usb-audio: Add native DSD quirks for PureAudio DAC series 2025-11-14 14:19:47 +01:00
tools RISC-V updates for v6.18-rc7 2025-11-22 09:44:50 -08:00
usr gen_init_cpio: Ignore fsync() returning EINVAL on pipes 2025-10-07 09:53:05 -07:00
virt KVM: guest_memfd: Remove bindings on memslot deletion when gmem is dying 2025-11-04 09:16:53 -08:00
.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 soc: fixes for 6.18, part 3 2025-11-19 09:36:04 -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 gpio fixes for v6.18-rc7 2025-11-21 10:43:58 -08:00
Makefile Linux 6.18-rc7 2025-11-23 14:53:16 -08:00
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.