Bulldozer for Servers: Testing AMD's "Interlagos" Opteron 6200 Series
by Johan De Gelas on November 15, 2011 5:09 PM ESTPower Management in Windows Server 2008 SP2
Enabling the C-states in ESX 5i might bring the Opteron 6276 an improved performance/watt ratio. The question is whether the low power consumption at light loads will negate the performance impact. Although power consumption is lowered by using the "C-state enable" tweak, it is not spectacular: 10% lower energy consumption in idle will probably not give the Opteron 6276 an amazing performance/watt ration in ESXi. The impact of this tweak will make a difference in our EWL testing, not in the "full speed ahead" benchmarks. Also, our vApus FOS EWL testing showed that the Xeon consumed 25% less energy, so it will remain ahead.
As the virtualization benchmarks require more time to run, we will have to delay investigating them for a later article. But what about Windows 2008 R2? The idle power of the Opteron 6276 was excellent there. So which power policy should be chosen in Windows 2008? We compared Opteron performance in "High performance" to the Opteron 6276 performance when the power management policy was set to "Balanced.
|
Opteron 6276 "High Performance" |
Opteron 6276 "High Performance" + C6 enable. |
Xeon X5670 "High performance" vs. Xeon X5670 "Balanced" |
|
| Cinebench Single-threaded | +16% | +18% | +1% |
| Cinebench Multi-threaded | +5% | +5% | +1% |
| Blender | +4% | +13% | +1% |
| Encryption/Decryption AES | +43% / +42% | +43% / +44% | +28% / +28% |
| Encryption/Decryption Twofish/Serpent | +8% / +8% | +8 / +8% | +0 / +0% |
| Compression/decompression | +9% / +4% | +9 / +4% | +0 / +2% |
If we combine the our idle power consumption measurements with these numbers, things get a lot clearer. The "balanced" power policy disables turbo. Therefore, the maximum performance boost from enabling "high performance" should be 13%. The TrueCrypt benchmarks show much larger increases (see (*)), which we honestly don't understand. The performance boost (40%) is only possible if the CPU boosts to 3.2GHz, but that is not supposed to happen. First, the TrueCrypt software is well threaded and uses all clusters (32 threads). Second, we disabled C6, so normally the CPU is not able to boost to 3.2GHz. Third, our monitoring clearly indicated a 2.6GHz clock as expected.
We also did a quick x264 4.0 benchmark (1st pass) which is lightly threaded and showed the same performance (46%!) increase by simply switching from "Balanced" to "High performance" (turbo limited to 2.6GHz, no C6). The Xeon only got a 13% increase in performance..
Closer monitoring reveals that "Balanced" frequently reduces the cores to 1.4GHz. So we have a similar situation as the one where we found power management problems on the AMD "Istanbul" Opteron when the power policy was set to "Balanced".
Basically "Balanced" brings the clock speed down to a low P-state even when a thread is demanding the maximum processing power. Or in other words, the power manager is too eager to bring the clock speed down instead of looking ahead: the polling is blind for the very near future. The result is that quite often the workload gets processed at 1.4GHz (for a short time).
In contrast, the high performance setting does not make use of frequency scaling besides Turbo. So the CPU runs at 2.3GHz at the very minimum and frequently reaches 2.6GHz. So if you buy an Opteron 6200 server, it is strongly advised to chose the "High Performance" setting. Under light load, the balanced power manager saves a few percentage of power running idle, but in our opinion, it is not worth the large performance degradation. Notice also that the Xeon hardly suffers from the same problem with the exception of the AES-NI enabled TrueCrypt bench, and even then the performance impact is significantly lower.
In a nutshell: the power policy "Balanced" strongly favors the Xeon as the performance impact is non-existent or much lower. Let us see some raw performance numbers.
Facebook
Twitter
RSS
106 Comments
View All Comments
JohanAnandtech - Thursday, November 17, 2011 - link
1) Niagara is NOT a CMT. It is interleaved multipthreading with SMT on top.
I haven't studied the latest Niagaras but the T1 was a fine grained mult-threaded CPU. It switched like a gatling gun between threads, and could not execute two threads at the same time.
Penti - Thursday, November 17, 2011 - link
SPARC T2 and onwards has additional ALU/AGU resources for a half physical two thread (four logically) solution per core with shared scheduler/pipeline if I remember correctly. That's not when CMT entered the picture according to SUN and Sun engineers any way. They regard the T1 as CMT as it's chip level. It's not just a CMP-chip any how. SMT is just running multiple threads on the cpus, CMP is working the same as SMP on separate sockets. It is not the same as AMDs solution however.Phylyp - Tuesday, November 15, 2011 - link
Firstly, this was a very good article, with a lot of information, especially the bits about the differences between server and desktop workloads.Secondly, it does seem that you need to tune either the software (power management settings) or the chip (CMT) to get the best results from the processor. So, what advise is AMD offering its customers in terms of this tuning? I wouldn't want to pony up hundreds of dollars to have to then search the web for little titbits like switching off CMT in certain cases, or enabling High-performance power management.
Thirdly, why is the BIOS reporting 32 MB of L2 cache instead of 8 MB?
mino - Wednesday, November 16, 2011 - link
No need for tuning - turbo is OS-independent (unless OS power management explicitly disables it aka Windows).Just disable the power management on the OS level (= high performance fro Windows) and you are good to go.
JohanAnandtech - Thursday, November 17, 2011 - link
The BIOS is simply wrong. It should have read 16 MB (2 orochi dies of 8 MB L3)gamoniac - Tuesday, November 15, 2011 - link
Thanks, Johan. I run HyperV on Windows Server 2008 R2 SP1 on Phonem II X6 (my workstation) and have noticed the same CPU issue. I previously fixed it by disabling AMD's Cool'n'Quiet BIOS setting. After switching to high performance increase my overall power usage by 9 watts but corrected the CPU capping issue you mentioned.Yet another excellent article from AnandTech. Well done. This is how I don't mind spending 1 hour of my precious evening time.
mczak - Tuesday, November 15, 2011 - link
L1 data and instruction cache are swapped (instruction is 8x64kB 2-way data is 16x16kB 4-way)L2 is 8x2MB 16-way
JohanAnandtech - Thursday, November 17, 2011 - link
fixed. My apologies.hechacker1 - Tuesday, November 15, 2011 - link
Curious if those syscalls for virtualization were improved at all. I remember Intel touting they improved the latency each generation.http://www.anandtech.com/show/2480/9
I'm guessing it's worse considering the increased general cache latency? I'm not sure how the latency, or syscall, is related if at all.
Just curious as when I do lots of compiling in a guest VM (Gentoo doing lots of checking of packages and hardware capabilities each compile) it tends to spend the majority of time in the kernel context.
hechacker1 - Tuesday, November 15, 2011 - link
Just also wanted to add: Before I had a VT-x enabled chip, it was unbearably slow to compile software in a guest VM. I remember measuring latencies of seconds for some operations.After getting an i7 920 with VT-x, it considerably improved, and most operations are in the hundred or so millisecond range (measured with latencytop).
I'm not sure how the latests chips fare.