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Desperate move by Intel. They are stuck with Cascade Lake until 2021, when their 'new' architecture will be available. In order this Xeon to be under 300W TDP,

Desperate move by Intel. They are stuck with Cascade Lake until 2021, when their 'new' architecture will be available. In order this Xeon to be under 300W TDP, they disabled the Hyper Threading and when they benchmark vs AMD Epyc they disabled AMD's SMT. Just wow.

Nimitz14 8y ago
Someone watches AdoredTV..
c2h5oh 8y ago
One theory is that the new xeon comes with no HT to keep the power draw under 300W, which is why the footnotes mention no HT/SMT in test configuration... This would also "fix" a lot of side channel attacks without new silicon being ready and Intel claims this CPU includes some hardware mitigations.
- nolok 8y ago
  It's still rather telling that they compare only with the equivalent also off on the AMD chip.
  - tutanchamun 8y ago
    Especially since AMDs SMT is better.
- rbanffy 8y ago
  It also doubles the effective amount of cache per core. I kind of like that.
  - xxs 8y ago
    do you mean the L2 or L3 cache? Hyperthreading is there to help reduce the times the CPU is stalled. If you run less active threads, the cache efficiency would the same in that case, hypethreading or not.
    - rbanffy 8y ago
      L1 and L2 (IIRC) are usually tied to a single physical core and, also IIRC, are partitioned between logical cores when HT is enabled. With HT disabled, cache per logical core doubles (because there is only one) and cache misses go down. Many HPC installs run with HT disabled because of that (YMMV depending on specifics of your workload - if your hot data fits in the cache, you'll be happy). Now that we mention it, I wonder if HT can be enabled or disabled per core. If that's possible, the machine would look like it has some logical cores with more cache than others and we could use cache miss counters as input to decide where a process should run.
      - xxs 8y ago
        >With HT disabled, cache per logical core doubles (because there is only one) and cache misses go down. This is too naive to look at in such a way. Yes if there is less scheduling on the core (less concurrency) the likehood of misses is lower, but the idea is to pay less for each miss doing effectively something else meanwhile instead of being stalled for memory. >Now that we mention it, I wonder if HT can be enabled or disabled per core. OS scheduler can do that. Normally the guidance for hyperthreading is: consider each "thread" as a separate core. If an OS chooses to use one core at a time and not schedule anything, the hypertrheadind won't be used. That is imagine logical core0&core 1 represent the same physical one, if the OS schedules only to core0, hyperthreading is not in play. Notes: controlling scheduling on linux is done via taskset. And cores info is available via "cat /proc/cpuinfo"
        rbanffy 8y ago
        > OS scheduler can do that True, but the scheduler can't tell the CPU to allocate all of the partitioned cache to a thread if it the silicon thinks it belongs to another logical core, so you end with effectively half of your cache dark. If L1 and L2 are pooled between the logical cores, it makes no difference, but I'm not sure how HT behaves WRT to partitioning caches on current generations of Intel parts and I remember it used to be like that (because I turned off HT on a couple dozen boxes to improve single thread performance, which was what was bothering me).
- mtgx 8y ago
  I'll be one of those to say that HT/SMT should probably die off unless the chipmakers learn how to make it secure. I'd rather have twice the physical cores for a little higher price anyway. However, Intel starting to sell chips without HT has nothing to do with the insecurity of HT and everything to do with the fact that they are trying to sell chips that are cheaper to make (or more profitable), while also being a little more competitive (price-wise) with AMD's offerings. But while they do this, they know they'll have a severe handicap in performance as long as AMD continues to sell competing products with SMT enabled. So their "solution" is to start making it "fair" in their benchmarks by using only half the cores or the SMT disabled for competing AMD products. One of the first clues that tells us this move is not a response to the recent security vulnerabilities of HT is that they started offering chips without HT only a few months after those discoveries were made. Do you really think something like planning to design and ship a product without HT happened only a few months earlier? No, this was decided at least a year and a half ago.
  - snovv_crash 8y ago
    Not everyone runs programs they don't trust on hardware they don't own. These sidechannel attacks are really only an issue for consumers with JIT JavaScript, and for enterprise with shared hosting. For HPC, or consumer/professional applications eg. gaming, rendering, encoding, ie. all those places where performance actually really matters, SMT is a great way to get a decent boost in a lot of workloads.
    - marmaduke 8y ago
      It seems like something that should be improved at the OS-level, where some workloads are untrusted and can'tb e HT'd next to others, whereas trusted software can be.
  - toast0 8y ago
    I don't think we can know for sure why they disabled HT. There's arguments for both. It's certainly possible that during the long Spectre embargo, someone was looking around and realized HT was going to be a problem. It's also not that hard to disable HT -- it's a flag somewhere in the on chip settings, in some parts of their product line, it's already done as part of binning and market segmentation. It's just a matter of deciding to have more SKUs with that set. Actually removing the die space used for HT would be different, but then we'd see chip families released without HT in any SKU.
deleted 8y ago
[deleted]
xxs 8y ago
C'mon they removed 'only' the SMT, nothing like disabling half the cores of 2700x on the infamous 9900k launch game tests
- bryanlarsen 8y ago
  Disabling half the cores can be (poorly) justified. "We enabled game mode on the AMD 2700x, wasn't that what we should have done?"
TazeTSchnitzel 8y ago
It's also supposedly not an actual benchmark, just a projection of what the (not yet actually existing) chip should perform like. I would take the numbers with several bags of salt.
einr 8y ago
Not only that, but they also apparently recompiled Linpack with the Intel compiler -- which is notorious for favoring Intel chips -- before running the benchmarks. Some really shady stuff going on here.
- geezerjay 8y ago
  On the other hand, these shady practices are a testament to AMD's technical superiority, as the incumbent is showing himself to be very desperate to react although it has absolutely no answer to AMD's new line of products.
  - marmaduke 8y ago
    That's not something you can cite or point to when justifying a purchasing choice to $pointy_haired_boss
  - Koshkin 8y ago
    AMD does not have techinal superiority, as Intel cores have better single-thread performance. Look at the recent low-end i3-8100 - it is an amazing chip.
    - AnthonyMouse 8y ago
      But Intel won't even give that to you. The i3-8100 doesn't have turbo boost, which means it's stuck at 3.6GHz and typically doesn't have faster single thread performance than AMD's faster chips. If you want Intel to sell you the one that hits 5GHz you have to pay for more cores which, if all you care about is single thread performance, you can't even use.
    - api 8y ago
      Single-threaded performance is a toss up and depends on work load. Overall AMD beats them on price/performance and multithreaded performance, which matter more for everything but some games and a few not easily parallelize-able tasks.

Nimitz14 8y ago

Someone watches AdoredTV..

c2h5oh 8y ago

One theory is that the new xeon comes with no HT to keep the power draw under 300W, which is why the footnotes mention no HT/SMT in test configuration... This would also "fix" a lot of side channel attacks without new silicon being ready and Intel claims this CPU includes some hardware mitigations.

nolok 8y ago
It's still rather telling that they compare only with the equivalent also off on the AMD chip.
- tutanchamun 8y ago
  Especially since AMDs SMT is better.
rbanffy 8y ago
It also doubles the effective amount of cache per core. I kind of like that.
- xxs 8y ago
  do you mean the L2 or L3 cache? Hyperthreading is there to help reduce the times the CPU is stalled. If you run less active threads, the cache efficiency would the same in that case, hypethreading or not.
  - rbanffy 8y ago
    L1 and L2 (IIRC) are usually tied to a single physical core and, also IIRC, are partitioned between logical cores when HT is enabled. With HT disabled, cache per logical core doubles (because there is only one) and cache misses go down. Many HPC installs run with HT disabled because of that (YMMV depending on specifics of your workload - if your hot data fits in the cache, you'll be happy). Now that we mention it, I wonder if HT can be enabled or disabled per core. If that's possible, the machine would look like it has some logical cores with more cache than others and we could use cache miss counters as input to decide where a process should run.
    - xxs 8y ago
      >With HT disabled, cache per logical core doubles (because there is only one) and cache misses go down. This is too naive to look at in such a way. Yes if there is less scheduling on the core (less concurrency) the likehood of misses is lower, but the idea is to pay less for each miss doing effectively something else meanwhile instead of being stalled for memory. >Now that we mention it, I wonder if HT can be enabled or disabled per core. OS scheduler can do that. Normally the guidance for hyperthreading is: consider each "thread" as a separate core. If an OS chooses to use one core at a time and not schedule anything, the hypertrheadind won't be used. That is imagine logical core0&core 1 represent the same physical one, if the OS schedules only to core0, hyperthreading is not in play. Notes: controlling scheduling on linux is done via taskset. And cores info is available via "cat /proc/cpuinfo"
      - rbanffy 8y ago
        > OS scheduler can do that True, but the scheduler can't tell the CPU to allocate all of the partitioned cache to a thread if it the silicon thinks it belongs to another logical core, so you end with effectively half of your cache dark. If L1 and L2 are pooled between the logical cores, it makes no difference, but I'm not sure how HT behaves WRT to partitioning caches on current generations of Intel parts and I remember it used to be like that (because I turned off HT on a couple dozen boxes to improve single thread performance, which was what was bothering me).
mtgx 8y ago
I'll be one of those to say that HT/SMT should probably die off unless the chipmakers learn how to make it secure. I'd rather have twice the physical cores for a little higher price anyway. However, Intel starting to sell chips without HT has nothing to do with the insecurity of HT and everything to do with the fact that they are trying to sell chips that are cheaper to make (or more profitable), while also being a little more competitive (price-wise) with AMD's offerings. But while they do this, they know they'll have a severe handicap in performance as long as AMD continues to sell competing products with SMT enabled. So their "solution" is to start making it "fair" in their benchmarks by using only half the cores or the SMT disabled for competing AMD products. One of the first clues that tells us this move is not a response to the recent security vulnerabilities of HT is that they started offering chips without HT only a few months after those discoveries were made. Do you really think something like planning to design and ship a product without HT happened only a few months earlier? No, this was decided at least a year and a half ago.
- snovv_crash 8y ago
  Not everyone runs programs they don't trust on hardware they don't own. These sidechannel attacks are really only an issue for consumers with JIT JavaScript, and for enterprise with shared hosting. For HPC, or consumer/professional applications eg. gaming, rendering, encoding, ie. all those places where performance actually really matters, SMT is a great way to get a decent boost in a lot of workloads.
  - marmaduke 8y ago
    It seems like something that should be improved at the OS-level, where some workloads are untrusted and can'tb e HT'd next to others, whereas trusted software can be.
- toast0 8y ago
  I don't think we can know for sure why they disabled HT. There's arguments for both. It's certainly possible that during the long Spectre embargo, someone was looking around and realized HT was going to be a problem. It's also not that hard to disable HT -- it's a flag somewhere in the on chip settings, in some parts of their product line, it's already done as part of binning and market segmentation. It's just a matter of deciding to have more SKUs with that set. Actually removing the die space used for HT would be different, but then we'd see chip families released without HT in any SKU.

deleted 8y ago

[deleted]

xxs 8y ago

C'mon they removed 'only' the SMT, nothing like disabling half the cores of 2700x on the infamous 9900k launch game tests

bryanlarsen 8y ago
Disabling half the cores can be (poorly) justified. "We enabled game mode on the AMD 2700x, wasn't that what we should have done?"

TazeTSchnitzel 8y ago

It's also supposedly not an actual benchmark, just a projection of what the (not yet actually existing) chip should perform like. I would take the numbers with several bags of salt.

einr 8y ago

Not only that, but they also apparently recompiled Linpack with the Intel compiler -- which is notorious for favoring Intel chips -- before running the benchmarks. Some really shady stuff going on here.

geezerjay 8y ago
On the other hand, these shady practices are a testament to AMD's technical superiority, as the incumbent is showing himself to be very desperate to react although it has absolutely no answer to AMD's new line of products.
- marmaduke 8y ago
  That's not something you can cite or point to when justifying a purchasing choice to $pointy_haired_boss
- Koshkin 8y ago
  AMD does not have techinal superiority, as Intel cores have better single-thread performance. Look at the recent low-end i3-8100 - it is an amazing chip.
  - AnthonyMouse 8y ago
    But Intel won't even give that to you. The i3-8100 doesn't have turbo boost, which means it's stuck at 3.6GHz and typically doesn't have faster single thread performance than AMD's faster chips. If you want Intel to sell you the one that hits 5GHz you have to pay for more cores which, if all you care about is single thread performance, you can't even use.
  - api 8y ago
    Single-threaded performance is a toss up and depends on work load. Overall AMD beats them on price/performance and multithreaded performance, which matter more for everything but some games and a few not easily parallelize-able tasks.