Hi,
Steve Reinhardt schrieb:
3. With the new Beta2, m5 seems to use Root.clock as the reference tick
for all statistics. I stumbled over it because my CPI was suddenly
really huge (>500). This really shocked me until I realized that
Root.clock defaults to 1THz, so a CPI of 500 makes perfect sense for a
2GHz machine (once you know about it :-) ). Thus, the CPI in the stats
is no longer measured in processor cycles but in "root-cycles". Is this
a bug or a feature?
At the high level it's supposed to be a feature... there are times you
want to have components clocked at rates that are not integer
multiples of the CPU frequency. The CPU's CPI stat should divide out
its local clock rate though, so if it's not doing that then that's a
bug. FYI, internally we've been trying to make the distinction
between "clocks" (which are the local clocks for various components,
e.g. 2GHz for the CPU) and "ticks" (which is the global virtual time
rate, e.g. 1THz). We haven't fully renamed all the
flags/variables/options etc. to be consistent with this nomenclature,
but that's where we're headed.
Well, then this seems like a bug. This is how the CPI is currently
calculated:
cpi = simTicks / committedInsts;
Following your convention, this could rather be called "tpi = ticks per
instruction", or, as you suggested, the calculation should be something
like:
cpi = simTicks / committedInsts / clock;
Similarly, ipc needs to be changed.
BTW: should I post things like this to the bugtracker rather than to the ML?
Here's the diff
--- src/cpu/o3/cpu.cc.orig 2006-12-11 12:13:17.674351500 +0100
+++ src/cpu/o3/cpu.cc 2006-12-11 12:10:48.121005000 +0100
@@ -377,25 +377,25 @@
.name(name() + ".cpi")
.desc("CPI: Cycles Per Instruction")
.precision(6);
- cpi = simTicks / committedInsts;
+ cpi = simTicks / committedInsts / clock;
totalCpi
.name(name() + ".cpi_total")
.desc("CPI: Total CPI of All Threads")
.precision(6);
- totalCpi = simTicks / totalCommittedInsts;
+ totalCpi = simTicks / totalCommittedInsts / clock;
ipc
.name(name() + ".ipc")
.desc("IPC: Instructions Per Cycle")
.precision(6);
- ipc = committedInsts / simTicks;
+ ipc = committedInsts / simTicks * clock;
totalIpc
.name(name() + ".ipc_total")
.desc("IPC: Total IPC of All Threads")
.precision(6);
- totalIpc = totalCommittedInsts / simTicks;
+ totalIpc = totalCommittedInsts / simTicks * clock;
}
Jonas
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