On 9/26/14, 9:05 AM, Pawel Moll wrote:
To do the correlation you need both timestamps to be "taken"
simultaneously:
perf event user event
-----O--------------+-------------O------> t_mono
: | :
: V :
-----O----------------------------O------> t_perf
Of course it's not possible get both values literally at the same time,
but placing them in a atomic context a couple of instructions from each
other still gives pretty good results. The larger this distance is, the
An early patchset on this topic added the realtime clock as an event and an ioctl was used to push a sample into the event stream. In that case you have wall clock and perf-clock samples taken in the same kernel context and about as close together as you can get.
https://lkml.org/lkml/2011/2/27/158
https://lkml.org/lkml/2011/2/27/159
David