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The context associated with an ETM for a given perf event includes : - handle -> the perf output handle for the AUX buffer. - the path for the trace components - the buffer config for the sink. The path and the buffer config are part of the "aux_priv" data (etm_event_data) setup by the setup_aux() callback, and made available via perf_get_aux(handle). Now with a sink supporting IRQ, the sink could "end" an output handle when the buffer reaches the programmed limit and would try to restart a handle. This could fail if there is not enough space left the AUX buffer (e.g, the userspace has not consumed the data). This leaves the "handle" disconnected from the "event" and also the "perf_get_aux()" cleared. This all happens within the sink driver, without the etm_perf driver being aware. Now when the event is actually stopped, etm_event_stop() will need to access the "event_data". But since the handle is not valid anymore, we loose the information to stop the "trace" path. So, we need a reliable way to access the etm_event_data even when the handle may not be active. This patch replaces the per_cpu handle array with a per_cpu context for the ETM, which tracks the "handle" as well as the "etm_event_data". The context notes the etm_event_data at etm_event_start() and clears it at etm_event_stop(). This makes sure that we don't access a stale "etm_event_data" as we are guaranteed that it is not freed by free_aux() as long as the event is active and tracing, also provides us with access to the critical information needed to wind up a session even in the absence of an active output_handle. This is not an issue for the legacy sinks as none of them supports an IRQ and is centrally handled by the etm-perf. Cc: Mathieu Poirier <mathieu.poirier@linaro.org> Cc: Anshuman Khandual <anshuman.khandual@arm.com> Cc: Leo Yan <leo.yan@linaro.org> Cc: Mike Leach <mike.leach@linaro.org> Reviewed-by: Mike Leach <mike.leach@linaro.org> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com> Link: https://lore.kernel.org/r/20210405164307.1720226-16-suzuki.poulose@arm.com Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.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 Restructured Text 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.