x86, perf_counter, bts: Optimize BTS overflow handling

x86, perf_counter, bts: Optimize BTS overflow handling

Draining the BTS buffer on a buffer overflow interrupt takes too
long resulting in a kernel lockup when tracing the kernel.

Restructure perf_counter sampling into sample creation and sample
output.

Prepare a single reference sample for BTS sampling and update the
from and to address fields when draining the BTS buffer. Drain the
entire BTS buffer between a single perf_output_begin() /
perf_output_end() pair.

Signed-off-by: Markus Metzger <[email protected]>
Signed-off-by: Peter Zijlstra <[email protected]>
LKML-Reference: <20090915130023[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>