FreeBSD src
10c8755706
configtimer(). During normal operation "state->nextcallopt" will always be less than or equal to "state->nextcall" and checking only "state->nextcallopt" before calling "callout_process()" is sufficient. However when "configtimer()" is called a race might happen requiring both of these binary times to be checked. Short description of race: 1) A configtimer() call will reset both "state->nextcall" and "state->nextcallopt" to the same binary time. 2) If a "callout_reset()" call happens between "configtimer()" and the next "callout_process()" call, "state->nextcallopt" will get updated and "state->nextcall" will remain at the current time. Refer to logic inside cpu_new_callout(). 3) getnextcpuevent() only respects "state->nextcall" and returns this value over and over again, even if it is in the past, until "now >= state->nextcallopt" becomes true. Then these two time variables are corrected by a "callout_process()" call and the situation goes back to normal. The problem manifests itself in different ways. The common factor is the timer process(es) consume all CPU on one or more CPU cores for a long time, blocking other kernel processes from getting execution time. This can be seen by very high interrupt counts as displayed by "vmstat -i | grep timer" right after boot. When EARLY_AP_STARTUP was enabled in r310177 the likelyhood of hitting this bug apparently increased. Example output from "vmstat -i" before patch: cpu0:timer 7591 69 cpu9:timer 39031773 358089 cpu4:timer 9359 85 cpu3:timer 9100 83 cpu2:timer 9620 88 Example output from "vmstat -i" after patch: cpu0:timer 4242 34 cpu6:timer 5531 44 cpu3:timer 6450 52 cpu1:timer 4545 36 cpu9:timer 7153 58 Before the patch cpu9 in the example above, was spinning in a loop in order to reach 39 million interrupts just a few seconds after bootup. After the patch the timer interrupt counts are more or less consistent. Discussed with: mav @ Reported by: several people MFC after: 1 week Sponsored by: Mellanox Technologies |
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| cddl | ||
| contrib | ||
| crypto | ||
| etc | ||
| gnu | ||
| include | ||
| kerberos5 | ||
| lib | ||
| libexec | ||
| release | ||
| rescue | ||
| sbin | ||
| secure | ||
| share | ||
| sys | ||
| targets | ||
| tests | ||
| tools | ||
| usr.bin | ||
| usr.sbin | ||
| .arcconfig | ||
| .arclint | ||
| COPYRIGHT | ||
| LOCKS | ||
| MAINTAINERS | ||
| Makefile | ||
| Makefile.inc1 | ||
| Makefile.libcompat | ||
| ObsoleteFiles.inc | ||
| README | ||
| UPDATING | ||
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 http://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 http://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. 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: http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/synching.html