• David Ahern's avatar
    perf x86: revert 20b279 - require exclude_guest to use PEBS - kernel side · a706d965
    David Ahern authored
    This patch is brought to you by the letter 'H'.
    
    Commit 20b279 breaks compatiblity with older perf binaries when run with
    precise modifier (:p or :pp) by requiring the exclude_guest attribute to be
    set. Older binaries default exclude_guest to 0 (ie., wanting guest-based
    samples) unless host only profiling is requested (:H modifier). The workaround
    for older binaries is to add H to the modifier list (e.g., -e cycles:ppH -
    toggles exclude_guest to 1). This was deemed unacceptable by Linus:
    
    https://lkml.org/lkml/2012/12/12/570
    
    
    
    Between family in town and the fresh snow in Breckenridge there is no time left
    to be working on the proper fix for this over the holidays. In the New Year I
    have more pressing problems to resolve -- like some memory leaks in perf which
    are proving to be elusive -- although the aforementioned snow is probably why
    they are proving to be elusive. Either way I do not have any spare time to work
    on this and from the time I have managed to spend on it the solution is more
    difficult than just moving to a new exclude_guest flag (does not work) or
    flipping the logic to include_guest (which is not as trivial as one would
    think).
    
    So, two options: silently force exclude_guest on as suggested by Gleb which
    means no impact to older perf binaries or revert the original patch which
    caused the breakage.
    
    This patch does the latter -- reverts the original patch that introduced the
    regression. The problem can be revisited in the future as time allows.
    Signed-off-by: default avatarDavid Ahern <dsahern@gmail.com>
    Cc: Avi Kivity <avi@redhat.com>
    Cc: Gleb Natapov <gleb@redhat.com>
    Cc: Ingo Molnar <mingo@kernel.org>
    Cc: Jiri Olsa <jolsa@redhat.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Robert Richter <robert.richter@amd.com>
    Link: http://lkml.kernel.org/r/1356749767-17322-1-git-send-email-dsahern@gmail.com
    
    Signed-off-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
    a706d965