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SubjectRe: [PATCHSET 0/8] perf tools: Fix scalability problem on callchain merging (v4)

* Namhyung Kim <namhyung@kernel.org> wrote:

> Hello,
>
> This is a new version of callchain improvement patchset. I found and
> fixed bugs in the previous version. I verified that it produced
> exactly same output before and after applying rbtree conversion patch
> (#1). However after Frederic's new comm infrastructure patches are
> applied it'd be little different.
>
> The patches are on 'perf/callchain-v4' branch in my tree
>
> git://git.kernel.org/pub/scm/linux/kernel/git/namhyung/linux-perf.git
>
>
> Please test!
>
> Thanks,
> Namhyung
>
>
> Frederic Weisbecker (4):
> perf tools: Use an accessor to read thread comm
> perf tools: Add time argument on comm setting
> perf tools: Add new comm infrastructure
> perf tools: Compare hists comm by addresses
>
> Namhyung Kim (4):
> perf callchain: Convert children list to rbtree
> perf ui/progress: Add new helper functions for progress bar
> perf tools: Show progress on histogram collapsing
> perf tools: Get current comm instead of last one

> 31 files changed, 504 insertions(+), 177 deletions(-)

I pulled this into a test-branch and resolved the builtin-trace.c conflict
with tip:master.

I tried your new code out with Linus's testcase of a parallel kernel
build:

perf record -g -- make -j8 bzImage

The 'perf record' session went mostly fine except for lost events:

Kernel: arch/x86/boot/bzImage is ready (#25)
[ perf record: Woken up 553 times to write data ]
[ perf record: Captured and wrote 196.811 MB perf.data (~8598789 samples) ]
Warning:
Processed 2631982 events and lost 54 chunks!

Check IO/CPU overload!

So, for completeness I'll mention that perf fails in two ways here:

- UI bug: it prints some scary warnings about 'IO/CPU overload' but
does not give any idea what the user could do about it. At minimum it
should print something about increasing --mmap-pages. It should also
print the current value of --mmap-pages so that the user knows to what
value to increase it ...

- defaults bug: this isn't an extreme workload on an extreme box - it's
a relatively bog standard system with 8 cores and 16 CPUs. The kernel
build was mild as well, with -j8. So losing events in perf record is
absolutely unacceptable. A solution might be to automatically increase
the ring-buffer if -g is used, in expectation of a higher data rate.

Once perf record was done I had the ~200 MB perf.data - and the 'perf
report' session went much smoother than ever before: the analysis went
very quickly, it finished within 10 seconds and displayed a nice progress
bar. So this is entirely usable IMO.

One small 'perf report' annoyance is that during the analysis passes
missing symbol printouts flash in the TUI - without the user having a
chance to read them. So those messages should either linger, or be
displayed at a later stage, for example when the user is confronted with
non-resolved symbols like:

+ 28.63% cc1 cc1 [.] 0x00000000006a92cb ◆

that is the point where the message would be useful - but nothing
indicates at all that this is an undesirable symbol entry and nothing
helps the user what to do about it!

A solution might be to display non-intrusive messages about non-resolved
symbols when such a symbol is manipulated (its children are openened, or
annotation is attempted).

Here there is a second annoyance: on the detailed screen the 'annotate'
entry is simply missing when the symbol has not been resolved. If I hit
'a' on the symbol entry itself in the graph view, then sometimes
annotation works - sometimes it does not and there's no UI feedback
whatsoever why it's not working.

I'm not suggesting to change the keyboard flow - that is very smooth - but
display information about failed annotations in the status line at the
bottom of the screen would be very useful. Remember: it's _always_ an UI
bug if the user hits a key and absolutely nothing happens. At minimum a
low-key, non-intrusive 'key X not bound' message should appear in the
status line bottom. Deterministic action/reaction sequences are utterly
important when interacting with computers.

Anyway, very nice progress with the tree here!

Thanks,

Ingo
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