power: Add basic DVFS support for gem5

Adds DVFS capabilities to gem5, by allowing users to specify lists for
frequencies and voltages in SrcClockDomains and VoltageDomains respectively.
A separate component, DVFSHandler, provides a small interface to change
operating points of the associated domains.

Clock domains will be linked to voltage domains and thus allow separate clock,
but shared voltage lines.

Currently all the valid performance-level updates are performed with a fixed
transition latency as specified for the domain.

Config file example:
...
vd = VoltageDomain(voltage = ['1V','0.95V','0.90V','0.85V'])
tsys.cluster1.clk_domain.clock = ['1GHz','700MHz','400MHz','230MHz']
tsys.cluster2.clk_domain.clock = ['1GHz','700MHz','400MHz','230MHz']
tsys.cluster1.clk_domain.domain_id = 0
tsys.cluster2.clk_domain.domain_id = 1
tsys.cluster1.clk_domain.voltage_domain = vd
tsys.cluster2.clk_domain.voltage_domain = vd
tsys.dvfs_handler.domains = [tsys.cluster1.clk_domain,
                             tsys.cluster2.clk_domain]
tsys.dvfs_handler.enable = True

1 files changed, 8 insertions, 3 deletions

diff --git a/src/sim/VoltageDomain.py b/src/sim/VoltageDomain.py
index ad84d756b..d6ccf9979 100644
--- a/src/sim/VoltageDomain.py
+++ b/src/sim/VoltageDomain.py
@@ -42,6 +42,11 @@ from m5.params import *
 class VoltageDomain(SimObject):
     type = 'VoltageDomain'
     cxx_header = "sim/voltage_domain.hh"
-    # We use a default voltage of 1V to avoid forcing users to set it
-    # even if they are not interested in using the functionality
-    voltage = Param.Voltage('1V', "Operational voltage")
+
+    # Single or list of voltages for the voltage domain.  If only a single
+    # voltage is specified, it is used for all different frequencies.
+    # Otherwise, the number of specified voltges and frequencies in the clock
+    # domain (src/sim/ClockDomain.py) must match.  Voltages must be specified in
+    # descending order. We use a default voltage of 1V to avoid forcing users to
+    # set it even if they are not interested in using the functionality
+    voltage = VectorParam.Voltage('1V', "Operational voltage(s)")