RFR (M): 8188764: Obsolete AssumeMP and then remove all support for non-MP builds
david.holmes at oracle.com
Tue Sep 18 05:32:20 UTC 2018
As previously discussed in the RFC thread:
this change obsoletes the AssumeMP flag and removes the bulk of the
logic that is conditional on os::is_MP() as follows:
1. to gate the introduction of MP-specific features, notably memory barriers
The is_MP check is removed and we will always issue memory barriers
or pre-pend lock prefix etc.
2. to align certain patchable code sequences (method entry, call sites)
The is_MP is removed and we always align patchable locations.
3. to gate certain optimizations which are questionable on uniprocessors
These are psuedo-memory-barriers where we manufacture a data-dependency
instead of inserting mfence/lfence (x86 example). These are treated as
#1 and is_MP is removed.
4. to gate optimizations which are desirable on uniprocessors
(mutex/monitor short circuits)
These are spin controls and so is_MP remains.
I have not updated the about-to-be-removed Oracle ARM port code.
- Tiers 1 -3 (mach5)
Performance run TBD.
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