The idea here is to avoid a memory access and conditional branch per probe site. Instead, the probe is represented by an "unreachable" unconditional function call. asm goto is used to store the address of the probe site (represented by a no-op sled) and the address of the function call into a tracepoint record. Each SDT probe carries a list of tracepoints. When the probe is enabled, the no-op sled corresponding to each tracepoint is overwritten with a jmp to the corresponding label. The implementation uses smp_rendezvous() to park all other CPUs while the instruction is being overwritten, as this can't be done atomically in general. The compiler moves argument marshalling code and the sdt_probe() function call out-of-line, i.e., to the end of the function. Per gallatin@ in D43504, this approach has less overhead when probes are disabled. To make the implementation a bit simpler, I removed support for probes with 7 arguments; nothing makes use of this except a regression test case. It could be re-added later if need be. The approach taken in this patch enables some more improvements: 1. We can now automatically fill out the "function" field of SDT probe names. The SDT macros let the programmer specify the function and module names, but this is really a bug and shouldn't have been allowed. The intent was to be able to have the same probe in multiple functions and to let the user restrict which probes actually get enabled by specifying a function name or glob. 2. We can avoid branching on SDT_PROBES_ENABLED() by adding the ability to include blocks of code in the out-of-line path. For example: if (SDT_PROBES_ENABLED()) { int reason = CLD_EXITED; if (WCOREDUMP(signo)) reason = CLD_DUMPED; else if (WIFSIGNALED(signo)) reason = CLD_KILLED; SDT_PROBE1(proc, , , exit, reason); } could be written SDT_PROBE1_EXT(proc, , , exit, reason, int reason; reason = CLD_EXITED; if (WCOREDUMP(signo)) reason = CLD_DUMPED; else if (WIFSIGNALED(signo)) reason = CLD_KILLED; ); In the future I would like to use this mechanism more generally, e.g., to remove branches and marshalling code used by hwpmc, and generally to make it easier to add new tracepoint consumers without having to add more conditional branches to hot code paths. Reviewed by: Domagoj Stolfa, avg MFC after: 2 months Differential Revision: https://reviews.freebsd.org/D44483 |
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.cirrus-ci | ||
.github | ||
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 | ||
.cirrus.yml | ||
.clang-format | ||
.git-blame-ignore-revs | ||
.gitattributes | ||
.gitignore | ||
.mailmap | ||
CONTRIBUTING.md | ||
COPYRIGHT | ||
LOCKS | ||
MAINTAINERS | ||
Makefile | ||
Makefile.inc1 | ||
Makefile.libcompat | ||
Makefile.sys.inc | ||
ObsoleteFiles.inc | ||
README.md | ||
RELNOTES | ||
UPDATING |
FreeBSD Source:
This is the top level of the FreeBSD source directory.
FreeBSD is an operating system used to power modern servers, desktops, and embedded platforms. A large community has continually developed it for more than thirty years. Its advanced networking, security, and storage features have made FreeBSD the platform of choice for many of the busiest web sites and most pervasive embedded networking and storage devices.
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), config(8), FreeBSD handbook on building userland, and Handbook for kernels for more information, including setting make(1) variables.
For information on the CPU architectures and platforms supported by FreeBSD, see the FreeBSD website's Platforms page.
For official FreeBSD bootable images, see the release page.
Source Roadmap:
Directory | Description |
---|---|
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 | Commands and libraries under the GNU General Public License (GPL) or Lesser General Public License (LGPL). Please see gnu/COPYING and gnu/COPYING.LIB 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 (see sys/README.md). |
targets | Support for experimental DIRDEPS_BUILD |
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 FreeBSD Handbook.