How much power savings does switching from Xeon E5 v3 to v4 (Haswell to Broadwell) provide?
I have never found answer on this quesiton myself, but I got an opportunty to buy a pair of E5 v4 for $10 today, so here are the result of this experiment:
Replacing
- 2x Xeon E5-2680 V3 2.5GHz 12-Core (total 24 cores, 48 threads) with
- 2x Xeon E5-2637 V4 3.5GHz 4-Core (total 8 cores, 16 threads):
reduced idle-ish (stroagenodes, plex, various jails, etc, but no nfs/smb transfers) power consumption from 212W to 195Watts (17 watts savings). Break even time: 2 months ($.52 kWh electric cost)
Higher max clocks and slightly higher IPC allowed to no longer bottleneck single-user NFS and SMB transfers.
But wait, there is more. Broadwellās killer feature is HWPM.
Results:
-
Freebsd/powerd/powerd++ lost all control over the CPU frequencies and CStates (
frequency control driver not supported: hwpstate_intel0
); albeit it wasnāt seeing beyoung C2 for some reason anyway, hence research deeper into the config.Oops!
% sudo powerdxx -fv -n adaptive powerd++: cannot read hw.acpi.acline powerd++: (EDRIVER) frequency control driver not supported: hwpstate_intel0
-
Varying load I now observe each CPU clock frequency change independently, unlike what was achievable with powerd/powerd++)
Nice!
dev.cpu.15.freq: 3598 dev.cpu.13.freq: 3598 dev.cpu.11.freq: 1197 dev.cpu.9.freq: 3598 dev.cpu.14.freq: 3598 dev.cpu.12.freq: 3598 dev.cpu.10.freq: 1197 dev.cpu.8.freq: 3598 dev.cpu.7.freq: 3598 dev.cpu.5.freq: 1197 dev.cpu.3.freq: 3598 dev.cpu.1.freq: 3598 dev.cpu.6.freq: 3598 dev.cpu.4.freq: 1197 dev.cpu.2.freq: 1396 dev.cpu.0.freq: 1498
-
Idle-ish power consumption further dropped to about 188 watts:I expected this to be slightly better ā and it somewhat is.
With this, total power savings is 24 Watts, or $9/month. So break even time is just one month, not two
Biggest bonus so far ā copying data over SMB is now goes just as fast, but at lower power ā I think because not all cores spin up when just one is enough.
Note, this is on FreeBSD 13. Linux has much better built-in power management, so likely you wonāt see such a dramatic power savings.