arch-arm: Memoize computeAddrTop in the MMU code
Profiling gem5 has indicated computeAddrTop as one of the main
contributors in AArch64 simulation time
The utility function gets used in the critical path of gem5, which is
the memory translation subsystem. The function is supposed to compute a
rather trivial task: identifying the "real" most significant bit of a
virtual address.
This turns out to be quite expensive. Why?
The main issue is the AArch32/AArch64 check, which uses the ELIs32
helper. This performs a sequential read of several MiscReg
values until it confirms that an EL is indeed using AArch32 (or
AArch64).
This is functionally accurate but it is too expensive for the critical
path of a program.
This patch is addressing the issue by adding a Memoizer object for the
computeAddrTop function to the CachedState data structure, which is
already holding cached system register values for performance reasons.
Whenever we need to invalidate those sys reg values because of a change
in the translation system, we also flush/invalidate the memoizer cache
Change-Id: If42e945c650c293ace304fb4c35e709783bb82d4
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/59151
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
2 files changed
