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A perf_event can be set up to deliver overflow notifications via SIGIO signal. The setup of the event is: 1. create event with perf_event_open() 2. assign it a signal for I/O notification with fcntl() 3. Install signal handler and consume samples The initial setup of perf_event_open() determines the period/frequency time span needed to elapse before each signal is delivered to the user process. While the event is active, system call ioctl(.., PERF_EVENT_IOC_PERIOD, value) can be used the change the frequency/period time span of the active event. The remaining signal handler invocations honour the new value. This does not work on s390. In fact the time span does not change regardless of ioctl's third argument 'value'. The call succeeds but the time span does not change. Support this behavior and make it common with other platforms. This is achieved by changing the interval value of the sampling control block accordingly and feed this new value every time the event is enabled using pmu_event_enable(). Before this change the interval value was set only once at pmu_event_add() and never changed. Signed-off-by: Thomas Richter <tmricht@linux.ibm.com> Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
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.