From: Paul Mackerras Date: Mon, 23 Mar 2009 17:22:08 +0000 (+0100) Subject: perf_counter: add an mmap method to allow userspace to read hardware counters X-Git-Tag: v2.6.31-rc1~383^2~449 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=37d81828385f8ff823caaaf1a83e72d065b6cfa1;p=pandora-kernel.git perf_counter: add an mmap method to allow userspace to read hardware counters Impact: new feature giving performance improvement This adds the ability for userspace to do an mmap on a hardware counter fd and get access to a read-only page that contains the information needed to translate a hardware counter value to the full 64-bit counter value that would be returned by a read on the fd. This is useful on architectures that allow user programs to read the hardware counters, such as PowerPC. The mmap will only succeed if the counter is a hardware counter monitoring the current process. On my quad 2.5GHz PowerPC 970MP machine, userspace can read a counter and translate it to the full 64-bit value in about 30ns using the mmapped page, compared to about 830ns for the read syscall on the counter, so this does give a significant performance improvement. Signed-off-by: Paul Mackerras Signed-off-by: Peter Zijlstra Orig-LKML-Reference: <20090323172417.297057964@chello.nl> Signed-off-by: Ingo Molnar --- Reading git-diff-tree failed