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For what it's worth, Intel is still faster in most applications, simply by virtue of having a clock speed advantage that by far exceeds any IPC difference, and

For what it's worth, Intel is still faster in most applications, simply by virtue of having a clock speed advantage that by far exceeds any IPC difference, and also by having much lower memory latencies. AMD has basically a 20-30 ns extra latency over Intel; so with good memory you can do ~45 ns on current Intels, but that will give you ~65 ns on a Ryzen. That's significant for a lot of code (e.g. pointer chasing, complex logic etc.). On the other hand, few applications scale efficiently to more than just four cores. Yes, of course, AMD delivers more Cinebenchpoints-per-Dollar and usually more Cinebenchpoints overall, but that's not necessarily an interesting metric. Personally I find that if I'm waiting on something to complete that the application in question tends to use only a tiny number of cores for the task at hand. Usually one. Another significant weakness of AMD's current platform is idle power consumption. These factors leave me with a much more nuanced impression than "Intel is ded" or "HOW IS INTEL GOING TO CATCH UP TO THIS????"; CPU reviews these days are just pure clickbait.

highfrequency 6y ago
Hi, this is very informative. To clarify a couple points: - By memory latency, do you mean the time to access an uncached portion of RAM? - RE clock speed advantage, are you referring to the fact that AMD turbo boost doesn't hit 5GHz?
- blattimwind 6y ago
  IIRC L3 is slightly slower on Zen 2, main memory as mentioned much slower. Clock speed advantage -- Most Zen 2 CPUs don't overclock to 4.5 GHz on any core, let alone all-core. The boost numbers are reached with current firmware, but only for tiniest fractions of a second and never under any real load. Sustained single-core boost frequencies are 200-400 MHz lower than the specified boost frequency. On the other hand, Intel CPUs consistently reach their boost frequencies under load, and most CPUs can do their single-core boost as an all-core overclock under load (with much greater power consumption of course). In practice this means that for equivalently priced parts (e.g. 3900X vs 10900K) the AMD part will have about a GHz lower clock for lightly threaded workloads, which are most workloads. With Intel settings, the Intel and AMD parts have about the same sustained clocks (3.8-4 GHz) under all-core load, but with the defaults of many motherboards the Intel part will run at 4.8-5 GHz, depending on the cooling.
  - gruez 6y ago
    >In practice this means that for equivalently priced parts (e.g. 3900X vs 10900K) the AMD part will have about a GHz lower clock for lightly threaded workloads They're only "equivalently priced" when you're talking about MSRP. Right now the 3900X sells for $413 and is in stock, whereas the i9-10900k sells for $530 and is out of stock.
    - deleted 6y ago
      [deleted]
jchw 6y ago
The problem is a lot of tasks that people want their CPU to be fast at is exactly stuff that parallelizes almost embarrassingly well. Compiling code, video rendering, compressing files. People buying CPUs for this are not as concerned about how many cycles it takes to jump through a vtable as long as its not slow. Meanwhile, pointing at memory latency as the flaw in Ryzen has been a popular misdirection for a while now. People warned me about it being a performance pitfall since before I bought my first Ryzen processor. In practice it doesn’t show up in even the most complexity intensive workloads as a serious issue. For example, Zen 2 performs very well on hardware emulation. This is possibly because where it takes a hit in memory latency it makes up in caching and prefetching, but honestly I don’t know and I am not sure how to measure. In any case it’s certainly favorably comparable to Intel’s best chipsets in single core workloads even if not on top. Factor in price and multicore workloads and you now have the exact reasons why people like me have been singing the praises... Intel’s single core lead may exist in some form but it is not what it once was, it is not an unconditional lead where an Intel core beats an AMD core. Not even close. None of this means Intel’s dead of course, but IMO thats mostly because they have a lot more going on than just being the best CPU. They’ve got their dedicated GPU coming out, and plenty of ancillary technology as well. It does seem like for a company like Intel having to take a backseat in CPUs for a while will be painful; unlike AMD, this is a new position for Intel and maybe not one they will handle well.
- lend000 6y ago
  You can get an idea of how popular different processors are in the server space by looking at the AWS EC2 spot market. Top end Xeon server processors (C5 and Z1d) typically have much lower spot discounts than AMD EPYC based processors (r5ad), although ARM c6g instances have been pushed up in price significantly over the last few months, perhaps as people switch over to them for the per-computational-unit cost savings. Of course, this is all a factor of Amazon's supply of instances and their chosen on-demand pricing level, but the trends are certainly interesting, and show steady demand for fast Xeon's and increasing demand for ARM's. I have run some compute heavy workloads on the best AMD's I could find on AWS and the speed difference per core for my particular workload was nearly 50%, which got worse as it scaled up to bigger instances because my workload uses a lot of L3 cache. I hear about EPYC's with 256MB of L3 cache but I can't seem to find those on AWS -- only ones with 8MB of cache.
dralley 6y ago
>Intel is still faster in most applications, simply by virtue of having a clock speed advantage that by far exceeds any IPC difference This is already only marginally true, the difference is only about 5% depending on the application, and in some applications AMD comes out ahead anyway. Expect the remaining difference to disappear when Zen 3 releases in a few months. >Another significant weakness of AMD's current platform is idle power consumption. AMD seems to have caught up here almost entirely. They've done a lot of work to improve idle power consumption lately and the node advantage probably helps, too.

highfrequency 6y ago

Hi, this is very informative. To clarify a couple points: - By memory latency, do you mean the time to access an uncached portion of RAM? - RE clock speed advantage, are you referring to the fact that AMD turbo boost doesn't hit 5GHz?

blattimwind 6y ago
IIRC L3 is slightly slower on Zen 2, main memory as mentioned much slower. Clock speed advantage -- Most Zen 2 CPUs don't overclock to 4.5 GHz on any core, let alone all-core. The boost numbers are reached with current firmware, but only for tiniest fractions of a second and never under any real load. Sustained single-core boost frequencies are 200-400 MHz lower than the specified boost frequency. On the other hand, Intel CPUs consistently reach their boost frequencies under load, and most CPUs can do their single-core boost as an all-core overclock under load (with much greater power consumption of course). In practice this means that for equivalently priced parts (e.g. 3900X vs 10900K) the AMD part will have about a GHz lower clock for lightly threaded workloads, which are most workloads. With Intel settings, the Intel and AMD parts have about the same sustained clocks (3.8-4 GHz) under all-core load, but with the defaults of many motherboards the Intel part will run at 4.8-5 GHz, depending on the cooling.
- gruez 6y ago
  >In practice this means that for equivalently priced parts (e.g. 3900X vs 10900K) the AMD part will have about a GHz lower clock for lightly threaded workloads They're only "equivalently priced" when you're talking about MSRP. Right now the 3900X sells for $413 and is in stock, whereas the i9-10900k sells for $530 and is out of stock.
  - deleted 6y ago
    [deleted]

jchw 6y ago

The problem is a lot of tasks that people want their CPU to be fast at is exactly stuff that parallelizes almost embarrassingly well. Compiling code, video rendering, compressing files. People buying CPUs for this are not as concerned about how many cycles it takes to jump through a vtable as long as its not slow. Meanwhile, pointing at memory latency as the flaw in Ryzen has been a popular misdirection for a while now. People warned me about it being a performance pitfall since before I bought my first Ryzen processor. In practice it doesn’t show up in even the most complexity intensive workloads as a serious issue. For example, Zen 2 performs very well on hardware emulation. This is possibly because where it takes a hit in memory latency it makes up in caching and prefetching, but honestly I don’t know and I am not sure how to measure. In any case it’s certainly favorably comparable to Intel’s best chipsets in single core workloads even if not on top. Factor in price and multicore workloads and you now have the exact reasons why people like me have been singing the praises... Intel’s single core lead may exist in some form but it is not what it once was, it is not an unconditional lead where an Intel core beats an AMD core. Not even close. None of this means Intel’s dead of course, but IMO thats mostly because they have a lot more going on than just being the best CPU. They’ve got their dedicated GPU coming out, and plenty of ancillary technology as well. It does seem like for a company like Intel having to take a backseat in CPUs for a while will be painful; unlike AMD, this is a new position for Intel and maybe not one they will handle well.

lend000 6y ago
You can get an idea of how popular different processors are in the server space by looking at the AWS EC2 spot market. Top end Xeon server processors (C5 and Z1d) typically have much lower spot discounts than AMD EPYC based processors (r5ad), although ARM c6g instances have been pushed up in price significantly over the last few months, perhaps as people switch over to them for the per-computational-unit cost savings. Of course, this is all a factor of Amazon's supply of instances and their chosen on-demand pricing level, but the trends are certainly interesting, and show steady demand for fast Xeon's and increasing demand for ARM's. I have run some compute heavy workloads on the best AMD's I could find on AWS and the speed difference per core for my particular workload was nearly 50%, which got worse as it scaled up to bigger instances because my workload uses a lot of L3 cache. I hear about EPYC's with 256MB of L3 cache but I can't seem to find those on AWS -- only ones with 8MB of cache.

dralley 6y ago

>Intel is still faster in most applications, simply by virtue of having a clock speed advantage that by far exceeds any IPC difference This is already only marginally true, the difference is only about 5% depending on the application, and in some applications AMD comes out ahead anyway. Expect the remaining difference to disappear when Zen 3 releases in a few months. >Another significant weakness of AMD's current platform is idle power consumption. AMD seems to have caught up here almost entirely. They've done a lot of work to improve idle power consumption lately and the node advantage probably helps, too.