Bug 409934

Summary:	Callgrind: Warning: L3 cache found, using its data for the LL simulation
Product:	[Developer tools] valgrind	Reporter:	jim.voulgaris
Component:	cachegrind	Assignee:	Nicholas Nethercote <njn>
Status:	REPORTED ---
Severity:	normal	CC:	jseward
Priority:	NOR
Version First Reported In:	unspecified
Target Milestone:	---
Platform:	Ubuntu
OS:	Linux
Latest Commit:		Version Fixed/Implemented In:
Sentry Crash Report:

Description jim.voulgaris 2019-07-18 07:32:10 UTC

SUMMARY
Callgrind allows cache simulation and also user-specified cache configuration. Regarding the latter and especially the --LL=<>,<>,<> flag I noticed that when an L3/L4 cache is discovered the following warning pops up "warning: L3 cache found, using its data for the LL simulation". However when callgrind's output (i.e. callgrind.out.<pid>) is read by callgrind_annotate it seems that the user-specified cache configuration has been used.

In my understanding the source code in file "cg_arch.c", where this warning is printed, does NOT override the user specifications in case of a HW L3/L4 cache is detected.

STEPS TO REPRODUCE
1. Run callgrind with --cache-sim=yes --LL=<>,<>,<>
2. Observe the warning that pops
3. Observe the output file using callgrind_annotate

OBSERVED RESULT
There is no coherence between the warning and the callgrind output result.

EXPECTED RESULT
The warning is wrongly printed.

SOFTWARE/OS VERSIONS
Windows: 
macOS: 
Linux/KDE Plasma: 
(available in About System)
KDE Plasma Version: 
KDE Frameworks Version: 
Qt Version: 

ADDITIONAL INFORMATION

Comment 1 Julian Seward 2019-12-28 16:36:13 UTC

My (limited) understanding of this is that, indeed, a --LL= specification
overrides whatever config info we might pull automatically from the hardware.