[Patch 0/1] HW-BKPT: Allow per-cpu kernel-space Hardware Breakpoint requests

K.Prasad
2009-08-17T12:46:55Z

Hi All,
Please find a patch that enables kernel-space breakpoints to be
requested for a subset of the available CPUs in the system. This allows
per-CPU breakpoints and comes with the associated benefit of reduced
overhead during (un)registration.

This enhancement allows exploitation of hardware breakpoint registers by
'perf' which produces a CPU-wise information.

Design changes
--------------
- Every breakpoint request 'consumes' the first available debug register
(starting from HBP_NUM) in each CPU represented by 'cpumask' field in
'struct hw_breakpoint'.

- 'hbp_kernel_pos' (that separates kernel-space breakpoints from the
free/user-space breakpoints) now points to the maximum of debug
registers consumed on any given CPU.
-- 'hbp_kernel_pos' is decremented (one-at-a-time) to allow a new-slot
for kernel-space requests iff all debug registers on the given CPU
(from HBP_NUM - 1 to 'hbp_kernel_pos' are already consumed.
-- 'hbp_kernel_pos' is incremented (one-at-a-time) to free a slot iff
a removal request results in the release of a bkpt request that
consumed maximum debug registers for kernel-space.

- Every removal request results in compaction of breakpoint registers
(on a per-cpu basis) to occupy the vacant debug register.

The patch is based on commit b6c720b811aed0eeda89f277f13c1bd1bdf721fd of
-tip tree and has been tested to work fine on an x86 machine for both
cases (i.e. system-wide kernel breakpoints and bkpts for a subset of CPUs).

Please let me know your comments on the same.

Thanks,
K.Prasad