mirror of
https://github.com/torvalds/linux.git
synced 2026-07-31 11:37:06 +02:00
Linux kernel source tree
74fd69a35c
The spinlock and rwlock use a single-element per-cpu array to track
current locks due to performance reason. But this means the key is
always available and it cannot simply account lock stats in the array
because some of them are invalid.
In fact, the contention_end() program in the BPF invalidates the entry
by setting the 'lock' value to 0 instead of deleting the entry for the
hashmap. So it should skip entries with the lock value of 0 in the
account_end_timestamp().
Otherwise, it'd have spurious high contention on an idle machine:
$ sudo perf lock con -ab -Y spinlock sleep 3
contended total wait max wait avg wait type caller
8 4.72 s 1.84 s 590.46 ms spinlock rcu_core+0xc7
8 1.87 s 1.87 s 233.48 ms spinlock process_one_work+0x1b5
2 1.87 s 1.87 s 933.92 ms spinlock worker_thread+0x1a2
3 1.81 s 1.81 s 603.93 ms spinlock tmigr_update_events+0x13c
2 1.72 s 1.72 s 861.98 ms spinlock tick_do_update_jiffies64+0x25
6 42.48 us 13.02 us 7.08 us spinlock futex_q_lock+0x2a
1 13.03 us 13.03 us 13.03 us spinlock futex_wake+0xce
1 11.61 us 11.61 us 11.61 us spinlock rcu_core+0xc7
I don't believe it has contention on a spinlock longer than 1 second.
After this change, it only reports some small contentions.
$ sudo perf lock con -ab -Y spinlock sleep 3
contended total wait max wait avg wait type caller
4 133.51 us 43.29 us 33.38 us spinlock tick_do_update_jiffies64+0x25
4 69.06 us 31.82 us 17.27 us spinlock process_one_work+0x1b5
2 50.66 us 25.77 us 25.33 us spinlock rcu_core+0xc7
1 28.45 us 28.45 us 28.45 us spinlock rcu_core+0xc7
1 24.77 us 24.77 us 24.77 us spinlock tmigr_update_events+0x13c
1 23.34 us 23.34 us 23.34 us spinlock raw_spin_rq_lock_nested+0x15
Fixes:
|
||
|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .editorconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| 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.