Package: intel-microcode
Version: 3.20151106.1~deb8u1
Some time after booting, all cores of an Intel E5-2680 v3 get throttled
to around 400MHz. The intel_pstate cpufreq driver is in use, as is the
powersave governor, but neither swapping to the performance governor nor
increasing CPU load recovers the expected clock speeds. This immense
loss of performance is new and highly undesirable behaviour.
Downgrading intel-microcode to 3.20150121.1 (microcode version 0x36 ->
0x32) restores the old behaviour, where core frequencies automatically
vary from around 1200MHz (quiescent) to 2800MHz (fully loaded).
When using the newer firmware package, behaviour is normal for several
hours before throttling occurs; on the occasion I have closely observed
/proc/cpuinfo the frequencies dropped after slightly under 3 hours, but
I don't know if that delay is strictly repeatable. On the two other
occasions I have booted with this firmware, performance was impacted
before 12 hours uptime.
The observed behaviour sounds similar to that in Launchpad bug #1506050.
Sample output of `grep MHz /proc/cpuinfo' when problem occurs:
cpu MHz : 426.269
cpu MHz : 441.113
cpu MHz : 425.878
cpu MHz : 440.039
cpu MHz : 448.828
cpu MHz : 449.902
cpu MHz : 447.851
cpu MHz : 447.851
cpu MHz : 452.636
cpu MHz : 441.796
cpu MHz : 470.605
cpu MHz : 438.085
cpu MHz : 573.632
cpu MHz : 428.906
cpu MHz : 423.632
cpu MHz : 404.394
cpu MHz : 409.375
cpu MHz : 417.187
cpu MHz : 380.078
cpu MHz : 444.531
cpu MHz : 408.691
cpu MHz : 405.175
cpu MHz : 564.843
cpu MHz : 525.488
Sample output of `grep MHz /proc/cpuinfo' under normal quiescent conditions:
cpu MHz : 1198.242
cpu MHz : 1225.585
cpu MHz : 1203.808
cpu MHz : 1200.878
cpu MHz : 1208.007
cpu MHz : 1225.097
cpu MHz : 1212.109
cpu MHz : 1198.242
cpu MHz : 1292.968
cpu MHz : 1207.714
cpu MHz : 1196.093
cpu MHz : 1207.226
cpu MHz : 1254.296
cpu MHz : 1209.667
cpu MHz : 1232.714
cpu MHz : 1202.832
cpu MHz : 1202.050
cpu MHz : 1201.074
cpu MHz : 1269.921
cpu MHz : 1200.878
cpu MHz : 1231.445
cpu MHz : 1208.203
cpu MHz : 1213.867
cpu MHz : 1200.585
Kernel: Linux 3.16.0-4-amd64 (3.16.7-ckt20-1+deb8u3)
Hardware: one Intel E5-2680 v3 in an Intel S2600WTT server board (other
socket unpopulated)
Regards, Stuart
