add load/store analysis

diff --git a/simple_v_extension.mdwn b/simple_v_extension.mdwn
index 70d994584b9f2c069a88a5738482b14278f89231..6ef54422dee82ea7f641732ea318c7051c22f556 100644 (file)
--- a/simple_v_extension.mdwn
+++ b/simple_v_extension.mdwn
@@ -79,14 +79,16 @@ P and V to make use of Compressed Instructions as a result.
 
 # Analysis and discussion of Vector vs SIMD
 
-There are five combined areas between the two proposals that help with
-parallelism without over-burdening the ISA with a huge proliferation of
+There are six combined areas between the two proposals that help with
+parallelism (increased performance, reduced power / area) without
+over-burdening the ISA with a huge proliferation of
 instructions:
 
 * Fixed vs variable parallelism (fixed or variable "M" in SIMD)
 * Implicit vs fixed instruction bit-width (integral to instruction or not)
 * Implicit vs explicit type-conversion (compounded on bit-width)
 * Implicit vs explicit inner loops.
+* Single-instruction LOAD/STORE.
 * Masks / tagging (selecting/preventing certain indexed elements from execution)
 
 The pros and cons of each are discussed and analysed below.
@@ -184,6 +186,20 @@ applied to embedded processors" (ZOLC), optimising only the single
 inner loop seems inadequate, tending to suggest that ZOLC may be
 better off being proposed as an entirely separate Extension.
 
+## Single-instruction LOAD/STORE
+
+In traditional Vector Architectures there are instructions which
+result in multiple register-memory transfer operations resulting
+from a single instruction.  They're complicated to implement in hardware,
+yet the benefits are a huge consistent regularisation of memory accesses
+that can be highly optimised with respect to both actual memory and any
+L1, L2 or other caches.
+
+Complications arise when Virtual Memory is involved: TLB cache misses
+need to be dealt with, as do page faults.  Some of the tradeoffs are
+discussed in <http://people.eecs.berkeley.edu/~krste/thesis.pdf>, Section
+4.6.
+
 ## Mask and Tagging (Predication)
 
 Tagging (aka Masks aka Predication) is a pseudo-method of implementing