sim: Adding support for power models

This patch adds some basic support for power models in gem5.

The power interface is defined so it can interact with thermal
models as well. It implements a simple power evaluator that
can be used for simple power models that express power in the
form of a math expression. These expressions can use stats
within the same SimObject (or down its hierarchy) and some
magic variables such as "temp" for temperature.
In future patches we will extend this functionality to allow
slightly more complex expressions.

The model allows it to be extended to use other kinds of models.

Change-Id: I76752f9638b6815e229fd74cdcb7721a305cbc4b

1 files changed, 177 insertions, 0 deletions

diff --git a/src/sim/mathexpr.cc b/src/sim/mathexpr.cc
new file mode 100644
index 000000000..d94639823
--- /dev/null
+++ b/src/sim/mathexpr.cc
@@ -0,0 +1,177 @@
+/*
+ * Copyright (c) 2016 ARM Limited
+ * All rights reserved
+ *
+ * The license below extends only to copyright in the software and shall
+ * not be construed as granting a license to any other intellectual
+ * property including but not limited to intellectual property relating
+ * to a hardware implementation of the functionality of the software
+ * licensed hereunder.  You may use the software subject to the license
+ * terms below provided that you ensure that this notice is replicated
+ * unmodified and in its entirety in all distributions of the software,
+ * modified or unmodified, in source code or in binary form.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met: redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer;
+ * redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution;
+ * neither the name of the copyright holders nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * Authors: David Guillen Fandos
+ */
+
+#include "sim/mathexpr.hh"
+
+#include <algorithm>
+#include <regex>
+#include <string>
+
+#include "base/misc.hh"
+
+MathExpr::MathExpr(std::string expr)
+ : ops(
+    std::array<OpSearch, uNeg + 1> {
+      OpSearch {true, bAdd, 0, '+', [](double a, double b) { return a + b; }},
+      OpSearch {true, bSub, 0, '-', [](double a, double b) { return a - b; }},
+      OpSearch {true, bMul, 1, '*', [](double a, double b) { return a * b; }},
+      OpSearch {true, bDiv, 1, '/', [](double a, double b) { return a / b; }},
+      OpSearch {false,uNeg, 2, '-', [](double a, double b) { return -b; }},
+      OpSearch {true, bPow, 3, '^', [](double a, double b) {
+                 return std::pow(a,b); }
+      },
+    })
+{
+    // Cleanup
+    expr.erase(remove_if(expr.begin(), expr.end(), isspace), expr.end());
+
+    root = MathExpr::parse(expr);
+    panic_if(!root, "Invalid expression\n");
+}
+
+/**
+ * This function parses a string expression into an expression tree.
+ * It will look for operators in priority order to recursively build the
+ * tree, respecting parenthesization.
+ * Constants can be expressed in any format accepted by std::stod, whereas
+ * variables are essentially [A-Za-z0-9\.$\\]+
+ */
+MathExpr::Node *
+MathExpr::parse(std::string expr) {
+    if (expr.size() == 0)
+        return NULL;
+
+    // From low to high priority
+    int par = 0;
+    for (unsigned p = 0; p < MAX_PRIO; p++) {
+        for (int i = expr.size() - 1; i >= 0; i--) {
+            if (expr[i] == ')')
+                par++;
+            if (expr[i] == '(')
+                par--;
+
+            if (par < 0) return NULL;
+            if (par > 0) continue;
+
+            for (unsigned opt = 0; opt < ops.size(); opt++) {
+                if (ops[opt].priority != p) continue;
+                if (ops[opt].c == expr[i]) {
+                    // Try to parse each side
+                    Node *l = NULL;
+                    if (ops[opt].binary)
+                        l = parse(expr.substr(0, i));
+                    Node *r = parse(expr.substr(i + 1));
+                    if ((l && r) || (!ops[opt].binary && r)) {
+                        // Match!
+                        Node *n = new Node();
+                        n->op = ops[opt].op;
+                        n->l = l;
+                        n->r = r;
+                        return n;
+                    }
+                }
+            }
+        }
+    }
+
+    // Remove trivial parenthesis
+    if (expr.size() >= 2 && expr[0] == '(' && expr[expr.size() - 1] == ')')
+        return parse(expr.substr(1, expr.size() - 2));
+
+    // Match a number
+    {
+        char *sptr;
+        double v = strtod(expr.c_str(), &sptr);
+        if (sptr != expr.c_str()) {
+            Node *n = new Node();
+            n->op = sValue;
+            n->value = v;
+            return n;
+        }
+    }
+
+    // Match a variable
+    {
+        bool contains_non_alpha = false;
+        for (auto & c: expr)
+            contains_non_alpha = contains_non_alpha or
+                !( (c >= 'a' && c <= 'z') ||
+                   (c >= 'A' && c <= 'Z') ||
+                   (c >= '0' && c <= '9') ||
+                   c == '$' || c == '\\' || c == '.' || c == '_');
+
+        if (!contains_non_alpha) {
+            Node * n = new Node();
+            n->op = sVariable;
+            n->variable = expr;
+            return n;
+        }
+    }
+
+    return NULL;
+}
+
+double
+MathExpr::eval(const Node *n, EvalCallback fn) const {
+    if (!n)
+        return 0;
+    else if (n->op == sValue)
+        return n->value;
+    else if (n->op == sVariable)
+        return fn(n->variable);
+
+    for (auto & opt : ops)
+        if (opt.op == n->op)
+            return opt.fn( eval(n->l, fn), eval(n->r, fn) );
+
+    panic("Invalid node!\n");
+    return 0;
+}
+
+std::string
+MathExpr::toStr(Node *n, std::string prefix) const {
+    std::string ret;
+    ret += prefix + "|-- " + n->toStr() + "\n";
+    if (n->r)
+        ret += toStr(n->r, prefix + "|   ");
+    if (n->l)
+        ret += toStr(n->l, prefix + "|   ");
+    return ret;
+}
+