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| author | Andreas Sandberg <Andreas.Sandberg@ARM.com> | 2013-04-22 13:20:32 -0400 |
|---|---|---|
| committer | Andreas Sandberg <Andreas.Sandberg@ARM.com> | 2013-04-22 13:20:32 -0400 |
| commit | f8f66fa3df3ef5b4e30ee86d33a4e95476ba425a (patch) | |
| tree | d3880f7bfda96783c2535d3e690026b6d6478efb /src/cpu/kvm/perfevent.hh | |
| parent | dc83d234254861f142854bdf523581101c3d5c8d (diff) | |
| download | gem5-f8f66fa3df3ef5b4e30ee86d33a4e95476ba425a.tar.xz | |
kvm: Add experimental support for a perf-based execution timer
Add support for using the CPU cycle counter instead of a normal POSIX
timer to generate timed exits to gem5. This should, in theory, provide
better resolution when requesting timer signals.
The perf-based timer requires a fairly recent kernel since it requires
a working PERF_EVENT_IOC_PERIOD ioctl. This ioctl has existed in the
kernel for a long time, but it used to be completely broken due to an
inverted match when the kernel copied things from user
space. Additionally, the ioctl does not change the sample period
correctly on all kernel versions which implement it. It is currently
only known to work reliably on kernel version 3.7 and above on ARM.
Diffstat (limited to 'src/cpu/kvm/perfevent.hh')
| -rw-r--r-- | src/cpu/kvm/perfevent.hh | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/src/cpu/kvm/perfevent.hh b/src/cpu/kvm/perfevent.hh index 8242cc071..eed900994 100644 --- a/src/cpu/kvm/perfevent.hh +++ b/src/cpu/kvm/perfevent.hh @@ -217,7 +217,8 @@ public: * like the new period isn't effective until after the next * counter overflow. If you use this method to change the sample * period, you will see one sample with the old period and then - * start sampling with the new period. + * start sampling with the new period. This problem was fixed for + * ARM in version 3.7 of the kernel. * * @warning This method doesn't work at all on some 2.6.3x kernels * since it has inverted check for the return value when copying |