On 29-01-23 14:31, Ivica B wrote:
Hi!
I am looking for a tool that can detect cache conflicts, but I am not
finding any. There are a few that are mostly academic, and thus not
maintained. I think it is important for the performance analysis
community to have a tool that to some extent can detect cache
conflicts. Is it possible to implement support for detecting source
code lines where cache conflicts occur? More info on cache conflicts
below.
[snip]
I agree that this is an interesting topic. If anyone else has ideas I'm
all ears.
My recommendations for this are:
1/ PMU/PMC (performance monitoring unit/counter) event counting tools
(perf record on Linux, pmcstat on FreeBSD, Oracle Studio collect on
Solaris, don't know for macOS). These can record events such as cache
misses with the associated callstacks. You can then use tools HotSpot
and perfgrind/kcachegrind (I hae used HotSpot but not perfgrind).
The big advantage of this is that the PMCs are part of the hardware and
the overhead of doing this is minor. The only slight limitation is that
then number of counters is limited.
2/ pahole
https://github.com/acmel/dwarves
A really nice binary analysis tool. It will analyze your binary (with
debuginfo) and generate a report for all structures showing holes,
padding and cache lines. It can even generate modified source with
members reordered to improve the packing. However as this is a static
tool working only on the data structures it knows nothing about your
access patterns.
3/ DHAT
One of the Valgrind tools. This profiles heap memory. If the block is
less than 1k it will also generate a kind of ascii-html heat map. That
map is an aggregate, but you can usually guess which offsets get hit the
most together.
Cachegrind doesn't really do this with the kind of accuracy that PMCs
do. It has a reduced model of the cache and has a basic branch
predictor. I don't know if or how speculative execution affects the
cache hit rate, but Valgrind doesn't do any of that.
A+
Paul
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