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A mirror of the official Linux kernel repository just in case
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Currently, IPIs are used to force other CPUs to invalidate their TLBs in response to a kernel virtual-memory mapping change. This works, but degrades both battery lifetime (for idle CPUs) and real-time response (for nohz_full CPUs), and in addition results in unnecessary IPIs due to the fact that CPUs executing in usermode are unaffected by stale kernel mappings. It would be better to cause a CPU executing in usermode to wait until it is entering kernel mode to do the flush, first to avoid interrupting usemode tasks and second to handle multiple flush requests with a single flush in the case of a long-running user task. This commit therefore reserves a bit at the bottom of the ->dynticks counter, which is checked upon exit from extended quiescent states. If it is set, it is cleared and then a new rcu_eqs_special_exit() macro is invoked, which, if not supplied, is an empty single-pass do-while loop. If this bottom bit is set on -entry- to an extended quiescent state, then a WARN_ON_ONCE() triggers. This bottom bit may be set using a new rcu_eqs_special_set() function, which returns true if the bit was set, or false if the CPU turned out to not be in an extended quiescent state. Please note that this function refuses to set the bit for a non-nohz_full CPU when that CPU is executing in usermode because usermode execution is tracked by RCU as a dyntick-idle extended quiescent state only for nohz_full CPUs. Reported-by: Andy Lutomirski <luto@amacapital.net> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org> |
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| Documentation | ||
| drivers | ||
| firmware | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. 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.