97e9382d56
search for a thread to steal inside a critical section. Since this allows the search to be preempted, restart the search if preemption happens since the search results found earlier may no longer be valid. Decrease the latency of starting a thread that may be assigned to this CPU during the search by polling for incoming threads during the search and switching to that thread instead of continuing the search. Test for stale search results and restart the search before going through the expense of calling tdq_lock_pair(). Retry some tests after grabbing the locks since things may have changed while waiting to get both locks. Eliminate special case handling for stealing from an SMT peer that uses 1 as the steal threshold. This can only succeed if a thread has been assigned but our SMT peer has not yet started executing it. This is quite rare and when it happens the other SMT thread is generally waiting for the same tdq lock that we hold. Basically both SMT threads are racing to grab the same spin lock. Add the kern.sched.always_steal knob from a ULE patch by jeff@. Incorporate another idea from Jeff's ULE patch. If the sched_switch() detects that the CPU is about to go idle, try to steal a thread before switching to the idle thread. Since the search for a thread to steal has to be done inside a critical section in this context, limit the impact on latency by adding the knob kern.sched.trysteal_limit to limit the topological distance of the search and don't restart the search if we detect stale results. If this search can't find an stealable thread, the idle loop can do a more complete search. Also poll for threads being assigned to this CPU during the search and switch to them instead of continuing the search. This change is responsibile for the majority of the improvement in parallel buildworld times. In sched_balance_group() change the minimum threshold from stealing a thread from 1 to 2. Poaching a newly assigned thread from a CPU that is waking up hasn't yet switched to that thread from idle is likely very rare and is likely to have the same lock race as is seen when stealing threads in the idle loop. Also use tdq_notify() to kick the destintation CPU instead of always sending an IPI. Update a stale comment, the number of transferable threads is not calculated. Reviewed by: kib (earlier version) Comments by: avg, jeff, mav MFC after: 1 month Differential Revision: https://reviews.freebsd.org/D12130 |
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| bin | ||
| cddl | ||
| contrib | ||
| crypto | ||
| etc | ||
| gnu | ||
| include | ||
| kerberos5 | ||
| lib | ||
| libexec | ||
| release | ||
| rescue | ||
| sbin | ||
| secure | ||
| share | ||
| stand | ||
| sys | ||
| targets | ||
| tests | ||
| tools | ||
| usr.bin | ||
| usr.sbin | ||
| .arcconfig | ||
| .arclint | ||
| .gitattributes | ||
| .gitignore | ||
| COPYRIGHT | ||
| LOCKS | ||
| MAINTAINERS | ||
| Makefile | ||
| Makefile.inc1 | ||
| Makefile.libcompat | ||
| Makefile.sys.inc | ||
| ObsoleteFiles.inc | ||
| README | ||
| README.md | ||
| UPDATING | ||
FreeBSD Source:
This is the top level of the FreeBSD source directory. This file
was last revised on:
FreeBSD
For copyright information, please see the file COPYRIGHT in this directory (additional copyright information also exists for some sources in this tree - please see the specific source directories for more information).
The Makefile in this directory supports a number of targets for building components (or all) of the FreeBSD source tree. See build(7) and https://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/makeworld.html for more information, including setting make(1) variables.
The buildkernel and installkernel targets build and install
the kernel and the modules (see below). Please see the top of
the Makefile in this directory for more information on the
standard build targets and compile-time flags.
Building a kernel is a somewhat more involved process. See build(7), config(8), and https://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/kernelconfig.html for more information.
Note: If you want to build and install the kernel with the
buildkernel and installkernel targets, you might need to build
world before. More information is available in the handbook.
The kernel configuration files reside in the sys/<arch>/conf
sub-directory. GENERIC is the default configuration used in release builds.
NOTES contains entries and documentation for all possible
devices, not just those commonly used.
Source Roadmap:
bin System/user commands.
cddl Various commands and libraries under the Common Development
and Distribution License.
contrib Packages contributed by 3rd parties.
crypto Cryptography stuff (see crypto/README).
etc Template files for /etc.
gnu Various commands and libraries under the GNU Public License.
Please see gnu/COPYING* for more information.
include System include files.
kerberos5 Kerberos5 (Heimdal) package.
lib System libraries.
libexec System daemons.
release Release building Makefile & associated tools.
rescue Build system for statically linked /rescue utilities.
sbin System commands.
secure Cryptographic libraries and commands.
share Shared resources.
stand Boot loader sources.
sys Kernel sources.
tests Regression tests which can be run by Kyua. See tests/README
for additional information.
tools Utilities for regression testing and miscellaneous tasks.
usr.bin User commands.
usr.sbin System administration commands.
For information on synchronizing your source tree with one or more of the FreeBSD Project's development branches, please see:
https://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/current-stable.html