tree f6bb9380e09100d33175b2a6d983b68b460817ad
parent cc6aa4c1739cbbb0ba2c8371f05e5af2a25f93dd
author Giacomo Travaglini <giacomo.travaglini@arm.com> 1649410205 +0100
committer Giacomo Travaglini <giacomo.travaglini@arm.com> 1651673096 +0000

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>