[petsc-users] cached values

Jed Brown jed at jedbrown.org
Sun Apr 26 19:13:04 CDT 2015

Justin Chang <jychang48 at gmail.com> writes:

> Jed,
> Thank you for the response. But where exactly are the values from
> MatSetValues() stored or located? That is, are they in main memory, or are
> they occupying space in the L1/L2/L3 cache?

Caches are not programmable in that way.  PETSc incrementally allocates
a data structure that holds the "stashed" values.  It depends on the
details of your application and the hardware cache semantics whether a
particular access will trigger a cache miss or not.  You can find out
using hardware performance counters, but it's not likely to be worth
your time unless you just want to learn those tools.
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