Update on Xeon W: Turbo Tablesby Ian Cutress on August 7, 2018 9:00 AM EST
- Posted in
- Turbo Boost
Last week we published our Xeon W review - Xeon W is the new name for Intel's Xeon E3-1600 series, but effectively replaces both the E5-1600 and E5-2600 chips that were commonly used in workstations. The new Xeon W line uses Skylake-X equivalent CPUs but enables ECC support for up to 512 GB of DRAM in a system, and while it uses the same LGA2066 socket as Skylake-X, due to product segmentation, Intel requires that the processors be used in a motherboard with an enterprise-grade C422 chipset.
You can read our full review here, where we tested a high, medium, and low-end CPU from the range, as well as the two quad-core parts that are officially 'off-roadmap'. In the review we go into what exactly 'off-roadmap' means.
The Intel Xeon W Review: W-2195, W-2155, W-2123, W-2104 and W-2102 Tested
One of the questions that came out of that review were the per-core turbo values for each processor. Intel has of late had a bifurcated strategy when it comes to disclosing turbo values: on the consumer line it does not disclose any turbo values any more, except single-core turbo, and on the enterprise lines they have fortunately been forthcoming with the data when asked. Although it isn't an automatic process to get the data, we are thankful that it does turn up. The point of this article is to state we finally have the turbo values for Xeon W.
Intel's per-core turbo data for these workstation parts are split up into three sections, due to the instruction sets they have. On the 'hardest' instructions, Intel uses special turbo values for AVX-512, as due to the way these instructions are processed, more heat is generated on chip. The chip has to balance frequency and power draw, so the AVX-512 data comes in at a lower frequency in order to keep the turbo in check.
The first thing to notice with this data is that for most CPUs, when the whole CPU is using AVX-512 instructions, the frequency will drop below the base frequency. For chips like the Xeon W-2123 and W-2133, even single core loading of AVX-512 will drop the frequency below the base frequency. Intel's base frequency does two things: first, it tells you the frequency at which TDP is applicable, and second it is the guaranteed minimum frequency for regular non-AVX instructions.
Behind AVX-512 is AVX2, which is still somewhat of a strain on the processor beyond regular instructions, but not as much. Where AVX-512 requires dedicated die area for support of the vector units, AVX2 is built into the back-end of the standard core design.
For AVX2, the W-2133 and W-2123 still end up below the base frequency of the processor. But for the big ones, like the W-2195, the full 18-core loading of AVX2 is 500 MHz faster than AVX-512. This is just an indication that users that are fine-tuning code should think about how much of the AVX-512 unit they can keep fed - the AVX-512 unit despite the 500 MHz difference is expected to be faster no doubt, but a half-fed AVX-512 might get trumped by a full AVX2.
For the regular instructions, turbo goes a bit like this:
For a number of users, the key metrics here are the all-core turbos, with the 18-core part having an all-core turbo of 3.2 GHz. Interestingly the W-2155 and W-2145 sits well here: for any code that can't reliably go beyond 12-14 threads, having the higher frequency but lower core count part might actually perform better. We saw a bit of this in our review, with the variable threaded loads executing somewhat better on the W-2155 than the W-2195.
We'll add this analysis to our main Xeon W review, but for those that requested the data, here it is! :)
- The Intel Xeon W Review: W-2195, W-2155, W-2123, W-2104 and W-2102 Tested
- The Supermicro X11SRA Motherboard Review: C422 based Workstation for Xeon-W
- HP Z4 Workstations Get Xeon W and Core X, 18-Core
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HStewart - Tuesday, August 7, 2018 - link"For a number of users, the key metrics here are the all-core turbos, with the 18-core part having an all-core turbo of 3.2 GHz. Interestingly the W-2155 and W-2145 sits well here: for any code that can't reliably go beyond 12-14 threads"
This is interesting statement - if multiply cores by all core frequency - even though the 18 core part is slower than 10 core - but if you need more thread 18 core will beat 10 core part even at higher frequency.
One thing interesting about Intel cores - with lower amount of core, will run faster other cores are not active.
But in general idea of recent ( last year or two ) increase in number of cores and actually application usage - what kind of applications use large amount of cores - and often does high amount of cores get used on system
jospoortvliet - Tuesday, August 7, 2018 - link
>This is interesting statement - if multiply cores by all core frequency - even though the 18 core part is slower than 10 core - but if you need more thread 18 core will beat 10 core part even at higher frequency.
What I find weird is that the higher core counts tend to have lower turbo's at similar active cores than the lower core count. So the 18 core is much slower than the 6 core if only 5 or 6 cores are active - 4 ghz vs 4.4! And if you load 10 cores, better buy the 10 core, because the 18 core would be running at only 2.8 ghz instead of the 3.3 of the 10 core!
That is very sad and frustrating - so the 18 core is only really faster if you actually use all of them, at a lower activity it is slower than smaller core counts. Why on earth is that? The other cores are off - why slow the ones that are on?
mode_13h - Tuesday, August 7, 2018 - linkProbably because it's designed for users who care about energy-efficiency and run apps that tend to have lots of concurrency.
Also, don't forget that cache coherency isn't free. Just because you're not running anything on those other cores doesn't mean it's as if they don't exist.
Finally, more cores means more mesh nodes between you and the memory controller. So, that's going to burn some power that could otherwise be used by a smaller chip to run at a higher speed.
GreenReaper - Wednesday, August 8, 2018 - linkAs the core count and last level cache increases, the base speed drops drastically. A big part of that is likely to be about staying within the TDP budget. 140W divided by 18 cores is less than 8W per core. While they can run for a time at 2.9Ghz eventually they have to throttle to 2.3Ghz.
Indeed, six cores might be more than 120W can handle if you look at the W-2133, if they're all running at 3.9/3.8Ghz. The W-2145 can only guarantee to run eight at 3.7Ghz.
"Off" isn't always _entirely_ off. There is still likely to be leakage, there may still be shared cache attached to the cores that needs to be accessible (high core count also tends to mean more cache), etc. The rings connecting the cores - or for newer HCC processors, the mesh - still needs to run. If nothing else it probably *was* on and will have heated the surrounding area up.
[That additional cache is one of the things which can makes the CPU faster in practice despite the fact that it might have to run at a lower clock speed. Mhz isn't everything.]
In an optimal world the CPU might know that *some* cores can go faster (e.g. core 5 can hit 4Ghz, but not cores 0-4 or 6-7) and be able to communicate this to the system, which could schedule work appropriately, but I don't think the current representation handles this.
In fact, nowadays CPU speeds can very so fast that the OS just sends hints about how power-efficient you want the CPU to be on each core and it sets its aggressiveness about ramping up and the maximum boost accordingly.
diehardmacfan - Tuesday, August 7, 2018 - linkSmall correction: Xeon-W is Intel's replacement for their E5 line, Xeon-E is their replacement for the E3 lineup.
HStewart - Tuesday, August 7, 2018 - link"Small correction: Xeon-W is Intel's replacement for their E5 line, Xeon-E is their replacement for the E3 lineup."
I don't believe that true - I believe Xeon-W are only single socket E5 supports more than one socket - like the following motherboard that supports 4 CPU's
Scalar able line is probably more in line E5 replacements
Xeon-W is a single cpu
and from the source
diehardmacfan - Tuesday, August 7, 2018 - linkJust depends on how you look at it i guess, If you want to say amount of supported CPU's supported are determining their lines then yes, you would need to go to Xeon-SP for more than one.
Their tiers went from Xeon E3, E5, E7 to E, W, SP. Xeon-W being the same socket as their HEDT lineup, like E5 was would also lend more credence to it.
HStewart - Tuesday, August 7, 2018 - linkXeons do have increase reliability over HEDT line - at lease when use my Dual Xeon - designed to run 24-7 and also for longer time - it been 10 years and only recently I stop using it. Dual 5160 primary because of incompatible with on board audio on Supermicro motherboard
Ian Cutress - Tuesday, August 7, 2018 - linkPeople put E5-2687W chips into single socket systems because they were workstation focused. Also the E5-2640 has been popular for cheap 8-core Intel systems
mode_13h - Tuesday, August 7, 2018 - link@dihardmacfan is right about this, with one footnote.
The W-series replaces the E5-1xxx chips. It's the E5-2xxx and above that support dual-CPU.