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5d95a2af97
Many of the the context reschedule users are of the form: ctx_sched_out(.type = EVENT_TIME); ... modify context ctx_resched(); With the idea that the whole reschedule happens with a single time-stamp, rather than with each ctx_sched_out() advancing time and ctx_sched_in() re-starting time, creating a non-atomic experience. However, Kan noticed that since this completely stops time, it actually looses a bit of time between the stop and start. Worse, now that we can do partial (per PMU) reschedules, the PMUs that are not scheduled out still observe the time glitch. Replace this with: ctx_time_freeze(); ... modify context ctx_resched(); With the assumption that this happens in a perf_ctx_lock() / perf_ctx_unlock() pair. The new ctx_time_freeze() will update time and sets EVENT_FROZEN, and ensures EVENT_TIME and EVENT_FROZEN remain set, this avoids perf_event_time_now() from observing a time wobble from not seeing EVENT_TIME for a little while. Additionally, this avoids loosing time between ctx_sched_out(EVENT_TIME) and ctx_sched_in(), which would re-set the timestamp. Reported-by: Kan Liang <kan.liang@linux.intel.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Kan Liang <kan.liang@linux.intel.com> Reviewed-by: Namhyung Kim <namhyung@kernel.org> Link: https://lore.kernel.org/r/20240807115550.250637571@infradead.org |
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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 reStructuredText 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.