d119357d07
The performance requirements on RCU Tasks, and in particular on RCU Tasks Trace, have evolved over time as the workloads have evolved. The current implementation is designed to provide low grace-period latencies, and also to accommodate short-duration floods of callbacks. However, current workloads can also provide a constant background callback-queuing rate of a few hundred call_rcu_tasks_trace() invocations per second. This results in continuous back-to-back RCU Tasks Trace grace periods, which in turn can consume the better part of 10% of a CPU. One could take the attitude that there are several tens of other CPUs on the systems running such workloads, but energy efficiency is a thing. On these systems, although asynchronous grace-period requests happen every few milliseconds, synchronous grace-period requests are quite rare. This commit therefore arrranges for grace periods to be initiated immediately in response to calls to synchronize_rcu_tasks*() and also to calls to synchronize_rcu_mult() that are passed one of the call_rcu_tasks*() functions. These are recognized by the tell-tale wakeme_after_rcu callback function. In other cases, callbacks are gathered up for up to about 250 milliseconds before a grace period is initiated. This results in more than an order of magnitude reduction in RCU Tasks Trace grace periods, with corresponding reduction in consumption of CPU time. Reported-by: Alexei Starovoitov <ast@kernel.org> Reported-by: Martin KaFai Lau <kafai@fb.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org> |
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| 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 | ||
| .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 Restructured Text 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.