https://bugs.kde.org/show_bug.cgi?id=420748
Bug ID: 420748
Summary: Excruciatingly slow loading of certain profiles
Product: kcachegrind
Version: unspecified
Platform: Archlinux Packages
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: general
Assignee: [email protected]
Reporter: [email protected]
Target Milestone: ---
FIRST THINGS FIRST
Please update kcachegrind version tags that are available for selection in this
bug report form. The version I am reporting this bug again is 20.04.0, and the
available versions are in their major zeros, so I am forced to select
"unspecified".
SECOND THINGS SECOND
This is a complicated bug and I will be reporting several aspects of it in
several places: kcachegrind, Xdebug, plasma, and whatever software artifact is
responsible for consuming and processing stderr from programs launched from
plasma desktop, either directly or via file association.
This happens to be the **first** of the places I am be reporting this, so
references to other bug reports are absent from the initial report, and will be
added in further comments.
STEPS TO REPRODUCE
1. Generate a large-ish (several tens of MB) profile with Xdebug
2. Have the profile file type associated with kcachegrind
3. Double click the profile file in Dolphin
OBSERVED RESULT
Kcachegrind starts and commences loading the profile, but loading is
excruciatingly slow.
EXPECTED RESULT
Loading should be fast.
SOFTWARE/OS VERSIONS
Operating System: Arch Linux
KDE Plasma Version: 5.18.4
KDE Frameworks Version: 5.69.0
Qt Version: 5.14.2
Kernel Version: 5.6.7-arch1-1
OS Type: 64-bit
Processors: 8 × AMD FX(tm)-8320 Eight-Core Processor
Memory: 15,6 GiB
ADDITIONAL INFORMATION
I have determined that the slowness is caused by large amount of stderr output
produced by the kcachegrind process while loading the profile. The stderr
output contains thousands of lines like this:
Loading "/[REDACTED]/cachegrind.out.ccnb" : 11601339 : "Garbage at end of
call cost line ('-2664')"
Loading "/[REDACTED]/cachegrind.out.ccnb" : 11601395 : "Garbage at end of
cost line ('-224')"
Loading "/[REDACTED]/cachegrind.out.ccnb" : 11601403 : "Garbage at end of
call cost line ('-224')"
Loading "/[REDACTED]/cachegrind.out.ccnb" : 11601491 : "Garbage at end of
call cost line ('-224')"
Loading "/[REDACTED]/cachegrind.out.ccnb" : 11601559 : "Garbage at end of
cost line ('-320')"
It appears that whatever is consuming stderr from programs launched via a file
association in plasma desktop, causes the process writing to stderr to block
for cumulatively significant amounts of time, or slows the producer process
down in some other way. This is definitely a problem on the consumer's end, and
I would greatly appreciate someone knowledgeable to advise where I should
report that problem.
This report however is about determining whether those "Garbage at end of(
call)? cost line" messages are valid in the first place. I don't think they
are. When I open the profile file in a text editor, I don't see any obvious
"garbage" in there. I believe that these messages may be caused by a bug in
kcachegrind.
This issue has been reported already in 2018 in Fedora bugtracker, but got
closed due to EOL of the Fedora version it was reported against:
https://bugzilla.redhat.com/show_bug.cgi?id=1537975
It may turn out that the profiles generated by Xdebug indeed contain garbage,
in which case I will be reporting this against Xdebug.
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