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SubjectRe: [GIT PULL] perf events changes for v3.4

* Linus Torvalds <torvalds@linux-foundation.org> wrote:

> On Mon, Mar 19, 2012 at 8:53 AM, Ingo Molnar <mingo@kernel.org> wrote:
> >
> > Please pull the latest perf-core-for-linus git tree from:
> >
> >   git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git perf-core-for-linus
>
> This seems to be another pull request that really could have
> done with some high-level overview of what the changes are for
> 3.4

Yeah, you are right, will do that next time around for the
larger trees (or trees that are not obviously single-topic at
first sight).

Here is a short (and incomplete) high-level summary of the perf
events changes of the v3.4 cycle:

- New "hardware based branch profiling" feature both on the
kernel and the tooling side, on CPUs that support it. (modern
x86 Intel CPUs with the 'LBR' hardware feature currently.)

This new feature is basically a sophisticated 'magnifying
glass' for branch execution - something that is pretty
difficult to extract from regular, function histogram centric
profiles.

The simplest mode is activated via 'perf record -b', and the
result looks like this in perf report:

$ perf record -b any_call,u -e cycles:u branchy

$ perf report -b --sort=symbol
52.34% [.] main [.] f1
24.04% [.] f1 [.] f3
23.60% [.] f1 [.] f2
0.01% [k] _IO_new_file_xsputn [k] _IO_file_overflow
0.01% [k] _IO_vfprintf_internal [k] _IO_new_file_xsputn
0.01% [k] _IO_vfprintf_internal [k] strchrnul
0.01% [k] __printf [k] _IO_vfprintf_internal
0.01% [k] main [k] __printf

This output shows from/to branch columns and shows the
highest percentage (from,to) jump combinations - i.e. the
most likely taken branches in the system. "branches" can also
include function calls and any other synchronous and
asynchronous transitions of the instruction pointer that are
not 'next instruction' - such as system calls, traps,
interrupts, etc.

This feature comes with (hopefully intuitive) flat ascii and
TUI support in perf report.

- Various 'perf annotate' visual improvements for us assembly
junkies. It will now recognize function calls in the TUI and
by hitting enter you can follow the call (recursively) and
back, amongst other improvements.

- Multiple threads/processes recording support in perf record,
perf stat, perf top - which is activated via a comma-list of
PIDs:

perf top -p 21483,21485
perf stat -p 21483,21485 -ddd
perf record -p 21483,21485

- Support for per UID views, via the --uid paramter to perf
top, perf report, etc. For example 'perf top --uid mingo'
will only show the tasks that I am running, excluding other
users, root, etc.

- Jump label restructurings and improvements - this
includes the factoring out of the (hopefully much clearer)
include/linux/static_key.h generic facility:

struct static_key key = STATIC_KEY_INIT_FALSE;

...

if (static_key_false(&key))
do unlikely code
else
do likely code

...
static_key_slow_inc();
...
static_key_slow_inc();
...

The static_key_false() branch will be generated into the code
with as little impact to the likely code path as possible.
the static_key_slow_*() APIs flip the branch via live kernel
code patching.

This facility can now be used more widely within the
kernel to micro-optimize hot branches whose likelihood
matches the static-key usage and fast/slow cost patterns.

- SW function tracer improvements: perf support and filtering
support.

- Various hardenings of the perf.data ABI, to make older
perf.data's smoother on newer tool versions, to make new
features integrate more smoothly, to support cross-endian
recording/analyzing workflows better, etc.

- Restructuring of the kprobes code, the splitting out of
'optprobes', and a corner case bugfix.

- Allow the tracing of kernel console output (printk).

- Improvements/fixes to user-space RDPMC support, allowing
user-space self-profiling code to extract PMU counts without
performing any system calls, while playing nice with the
kernel side.

- 'perf bench' improvements

- ... and lots of internal restructurings, cleanups and fixes
that made these features possible. And, as usual this list is
incomplete as there were also lots of other
improvements:

165 files changed, 6107 insertions(+), 1984 deletions(-)

Thanks,

Ingo
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