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peteraa 2019-10-17 16:59:16 +02:00
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@ -1,4 +1,36 @@
* Question 1 - Benchmarking
* Question 1 - Hazards
For the following program describe each hazard with type (data or control), line number and a
small (max one sentence) description
** program 1
#+begin_src asm
addi t0, zero, 10
addi t1, zero, 20
sub t1, t1, t0
beq t1, zero, .L2
jr ra
#+end_src
** program 2
#+begin_src asm
addi t0, zero, 10
lw t0, 10(t0)
beq t0, zero, .L3
jr ra
#+end_src
** program 3
#+begin_src asm
lw t0, 0(t0)
lw t1, 4(t0)
sw t0, 8(t1)
lw t1, 12(t0)
beq t0, t1, .L3
jr ra
#+end_src
* Question 2 - ???
* Question 3 - Benchmarking
In order to gauge the performance increase from adding branch predictors it is necessary to do some testing.
Rather than writing a test from scratch it is better to use the tester already in use in the test harness.
When running a program the VM outputs a log of all events, including which branches have been taken and which
@ -29,7 +61,7 @@
def helper(events: List[BranchEvent], predictionTable: Map[Int, Boolean]): Int = {
events match {
// Scala syntax for matching a list with a head element of some type and a tail
// Scala syntax for matching a list with a head element of some type and a tail
// `case h :: t =>`
// means we want to match a list with at least a head and a tail (tail can be Nil, so we
// essentially want to match a list with at least one element)
@ -42,11 +74,11 @@
// `case Constructor(arg1, arg2) :: t => if(p(arg1, arg2))`
// means we want to match a list whose first element is of type Constructor while satisfying some predicate p,
// called an if guard.
case Taken(addr) :: t if( predictionTable(addr)) => helper(t, predictionTable)
case Taken(addr) :: t if(!predictionTable(addr)) => 1 + helper(t, predictionTable.updated(addr, true))
case NotTaken(addr) :: t if(!predictionTable(addr)) => 1 + helper(t, predictionTable.updated(addr, false))
case NotTaken(addr) :: t if( predictionTable(addr)) => helper(t, predictionTable)
case _ => 0
case Taken(addr) :: t if( predictionTable(addr)) => helper(t, predictionTable)
case Taken(addr) :: t if(!predictionTable(addr)) => 1 + helper(t, predictionTable.updated(addr, true))
case NotTaken(addr) :: t if(!predictionTable(addr)) => 1 + helper(t, predictionTable.updated(addr, false))
case NotTaken(addr) :: t if( predictionTable(addr)) => helper(t, predictionTable)
case _ => 0
}
}
@ -60,6 +92,7 @@
}
#+END_SRC
** TODO Branch predictor is underspecified, needs to be cleaned up
** Your task
Your job is to implement a test that checks how many misses occur for a 2 bit branch predictor with 4 slots.
For this task it is probably smart to use something else than a ~Map[(Int, Boolean)]~
@ -70,7 +103,7 @@
With a 2 bit 4 slot scheme, how many misses will you incur?
Answer with a number.
* Question 2 - Cache profiling
* Question 4 - Cache profiling
Unlike our design which has a very limited memory pool, real designs have access to vast amounts of memory, offset
by a steep cost in access latency.
To amend this a modern processor features several caches where even the smallest fastest cache has more memory than