This patch enables very low-overhead access to high-resolution process virtual
time and, optionally, high-resolution virtualized user and system time.
If enabled, a page of memory containing timing values is allocated with each
task_struct, and an extra per-pid proc entry (/proc/PID/hrtime) is created
which, when mmapped, maps the timing page into the user's address space. All
process timing queries can be then be performed at memory reference speeds,
without the overhead of a system call. Timers work at the resolution of the
hardware timestamp counters. For convenience, a library is provided which can
be used to perform the mapping and timer querying.
In the current implementation, permissions on /proc/PID/hrtime are set to 400.
The library and the latest version of the patch against various 2.2 and 2.3
kernels is available at http://www.cs.wisc.edu/paradyn/libhrtime/. The
following patch is against 2.3.39
These timers were developed as part of the Paradyn Parallel Performance Tools
project at the University of Wisconsin.
-nick
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