linux/fs/erofs/Kconfig
Sandeep Dhavale 3fffb589b9 erofs: add per-cpu threads for decompression as an option
Using per-cpu thread pool we can reduce the scheduling latency compared
to workqueue implementation. With this patch scheduling latency and
variation is reduced as per-cpu threads are high priority kthread_workers.

The results were evaluated on arm64 Android devices running 5.10 kernel.

The table below shows resulting improvements of total scheduling latency
for the same app launch benchmark runs with 50 iterations. Scheduling
latency is the latency between when the task (workqueue kworker vs
kthread_worker) became eligible to run to when it actually started
running.
+-------------------------+-----------+----------------+---------+
|                         | workqueue | kthread_worker |  diff   |
+-------------------------+-----------+----------------+---------+
| Average (us)            |     15253 |           2914 | -80.89% |
| Median (us)             |     14001 |           2912 | -79.20% |
| Minimum (us)            |      3117 |           1027 | -67.05% |
| Maximum (us)            |     30170 |           3805 | -87.39% |
| Standard deviation (us) |      7166 |            359 |         |
+-------------------------+-----------+----------------+---------+

Background: Boot times and cold app launch benchmarks are very
important to the Android ecosystem as they directly translate to
responsiveness from user point of view. While EROFS provides
a lot of important features like space savings, we saw some
performance penalty in cold app launch benchmarks in few scenarios.
Analysis showed that the significant variance was coming from the
scheduling cost while decompression cost was more or less the same.

Having per-cpu thread pool we can see from the above table that this
variation is reduced by ~80% on average. This problem was discussed
at LPC 2022. Link to LPC 2022 slides and talk at [1]

[1] https://lpc.events/event/16/contributions/1338/

[ Gao Xiang: At least, we have to add this until WQ_UNBOUND workqueue
             issue [2] on many arm64 devices is resolved. ]
[2] https://lore.kernel.org/r/CAJkfWY490-m6wNubkxiTPsW59sfsQs37Wey279LmiRxKt7aQYg@mail.gmail.com

Signed-off-by: Sandeep Dhavale <dhavale@google.com>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20230208093322.75816-1-hsiangkao@linux.alibaba.com
2023-02-15 08:11:26 +08:00

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# SPDX-License-Identifier: GPL-2.0-only
config EROFS_FS
tristate "EROFS filesystem support"
depends on BLOCK
select FS_IOMAP
select LIBCRC32C
help
EROFS (Enhanced Read-Only File System) is a lightweight read-only
file system with modern designs (e.g. no buffer heads, inline
xattrs/data, chunk-based deduplication, multiple devices, etc.) for
scenarios which need high-performance read-only solutions, e.g.
smartphones with Android OS, LiveCDs and high-density hosts with
numerous containers;
It also provides fixed-sized output compression support in order to
improve storage density as well as keep relatively higher compression
ratios and implements in-place decompression to reuse the file page
for compressed data temporarily with proper strategies, which is
quite useful to ensure guaranteed end-to-end runtime decompression
performance under extremely memory pressure without extra cost.
See the documentation at <file:Documentation/filesystems/erofs.rst>
for more details.
If unsure, say N.
config EROFS_FS_DEBUG
bool "EROFS debugging feature"
depends on EROFS_FS
help
Print debugging messages and enable more BUG_ONs which check
filesystem consistency and find potential issues aggressively,
which can be used for Android eng build, for example.
For daily use, say N.
config EROFS_FS_XATTR
bool "EROFS extended attributes"
depends on EROFS_FS
default y
help
Extended attributes are name:value pairs associated with inodes by
the kernel or by users (see the attr(5) manual page, or visit
<http://acl.bestbits.at/> for details).
If unsure, say N.
config EROFS_FS_POSIX_ACL
bool "EROFS Access Control Lists"
depends on EROFS_FS_XATTR
select FS_POSIX_ACL
default y
help
Posix Access Control Lists (ACLs) support permissions for users and
groups beyond the owner/group/world scheme.
To learn more about Access Control Lists, visit the POSIX ACLs for
Linux website <http://acl.bestbits.at/>.
If you don't know what Access Control Lists are, say N.
config EROFS_FS_SECURITY
bool "EROFS Security Labels"
depends on EROFS_FS_XATTR
default y
help
Security labels provide an access control facility to support Linux
Security Models (LSMs) accepted by AppArmor, SELinux, Smack and TOMOYO
Linux. This option enables an extended attribute handler for file
security labels in the erofs filesystem, so that it requires enabling
the extended attribute support in advance.
If you are not using a security module, say N.
config EROFS_FS_ZIP
bool "EROFS Data Compression Support"
depends on EROFS_FS
select LZ4_DECOMPRESS
default y
help
Enable fixed-sized output compression for EROFS.
If you don't want to enable compression feature, say N.
config EROFS_FS_ZIP_LZMA
bool "EROFS LZMA compressed data support"
depends on EROFS_FS_ZIP
select XZ_DEC
select XZ_DEC_MICROLZMA
help
Saying Y here includes support for reading EROFS file systems
containing LZMA compressed data, specifically called microLZMA. it
gives better compression ratios than the LZ4 algorithm, at the
expense of more CPU overhead.
LZMA support is an experimental feature for now and so most file
systems will be readable without selecting this option.
If unsure, say N.
config EROFS_FS_ONDEMAND
bool "EROFS fscache-based on-demand read support"
depends on CACHEFILES_ONDEMAND && (EROFS_FS=m && FSCACHE || EROFS_FS=y && FSCACHE=y)
default n
help
This permits EROFS to use fscache-backed data blobs with on-demand
read support.
If unsure, say N.
config EROFS_FS_PCPU_KTHREAD
bool "EROFS per-cpu decompression kthread workers"
depends on EROFS_FS_ZIP
help
Saying Y here enables per-CPU kthread workers pool to carry out
async decompression for low latencies on some architectures.
If unsure, say N.
config EROFS_FS_PCPU_KTHREAD_HIPRI
bool "EROFS high priority per-CPU kthread workers"
depends on EROFS_FS_ZIP && EROFS_FS_PCPU_KTHREAD
help
This permits EROFS to configure per-CPU kthread workers to run
at higher priority.
If unsure, say N.