4 ms·

15-20w is never the peak TDP. They will actually hit as much as 50-60w with minimal GPU usage just from trying to hit that insane clockspeed. M1 maxed out at 2

by hajile 4y ago

15-20w is never the peak TDP. They will actually hit as much as 50-60w with minimal GPU usage just from trying to hit that insane clockspeed. M1 maxed out at 22w according to Anandtech and the max shouldn't be too much different for the M2.

kllrnohj 4y ago
[citation needed]
mkopec 4y ago
That's Intel's boost behavior, AMD is much more linear. My 4750U in performance mode never exceeds 25W and settles at 23W under sustained load.
- hajile 4y ago
  What device is that chip in and at what frequencies is it running (by number of cores in use)?
  - mkopec 4y ago
    Lenovo ThinkPad Gen1 AMD, Arch Linux, acpi platform_profile = performance When running stress-ng, measured with turbostat: - 4.18 GHz single thread consuming 9W - 3 GHz 16 threads consuming 25W, ramping down to 2.94 / 23W after a couple of seconds and when compiling Linux on 16 threads it stays at 2.85 GHz / 23W In performance mode it does run at 80 degC under sustained load, so usually when undocked I just leave it in balanced mode where it's capped at 20W short / 15W long Also worth noting is that in low-power mode (11W / 11W) it'll still hit max single core frequency possible.
bnieuwen 4y ago
Actually Phoronix has power benchmarks for the ACPI power profiles[1]. Seems like a boost to ~28W or so with a long term average of 22-23W. (Note that this is SoC package power instead of the full laptop though, but that is pretty typical, so no idea what the 22W was for comparison.) [1] https://www.phoronix.com/review/ryzen7-6850u-acpi https://www.phoronix.com/review/ryzen7-6850u-acpi
- hajile 4y ago
  I don't believe those numbers. The 4800U hit north of 65w in a NUC device[0]. The 5800U hits 52w in a laptop[1]. AMD runs their chips hot. TSMC N6 is a 7nm++ node. The even more advanced 5nm node only offers either 15% performance increase OR 30% power reduction vs N7. The 6850 clocks 10% higher, so the power shouldn't be dropping AT ALL. The 6850H has an identical turbo clockspeed of 4.7GHz and a TDP of 45w with real-world power consumption according to other reviewers being north of 65w. The base clocks for these chips is 2.7 and 3.5GHz respectively. In the case that they really are getting those numbers, they are certainly only at base clockspeeds (2.7GHz) which raises the impossible question of how Zen 3 suddenly got such a huge performance per clock advantage going from desktop to mobile. The numbers simply do not add up. [0] https://www.anandtech.com/show/16236/asrock-4x4-box4800u-renoir-nuc-review/11 https://www.anandtech.com/show/16236/asrock-4x4-box4800u-ren... [1] https://www.notebookcheck.net/R7-5800U-vs-E-2186M-vs-R7-PRO-5875U_12976_9902_14365.247596.0.html https://www.notebookcheck.net/R7-5800U-vs-E-2186M-vs-R7-PRO-...
  - wmf 4y ago
    Firmware can set the power limit to whatever it wants. With the exact same processor, one computer may hit 65 W while a different one is limited to 28 W. There's also huge diminishing utility when it comes to power, so it's possible that the chip is only slightly slower at 28 W than at higher power.
    - hajile 4y ago
      That diminishing return is much more true at 150w than at 50w. https://www.anandtech.com/show/16214/amd-zen-3-ryzen-deep-dive-review-5950x-5900x-5800x-and-5700x-tested/8 https://www.anandtech.com/show/16214/amd-zen-3-ryzen-deep-di... When you look at per-core performance of desktop chips, things aren't rosy. Looking at the 5950 (most power efficient per core), it's taking almost 7.5w PER CORE to hit 3.7GHz. It hits 4.7GHz (peak frequency of 6850U) on just 4 cores while using 110w to do it. That's almost 23w per core. Based on these numbers, taking 8 cores up to 3.7GHz would require 60w of power and that's just to hit the "base" frequencies of the 6850H which they say can be done with a TDP 25% lower than that (maybe dropping half the L3 cache makes that possible, but at an overall performance loss as moving stuff from RAM takes more energy than keeping it in L3 and I don't know that losing half the cache saves more energy than the addition of a GPU adds back to the chip). Even if we assume a 12% energy efficiency bump (two thirds of the 18% transistor reduction and roughly inline with the 30% efficiency at N5 with a 45% transistor reduction), we aren't doing anything multithreaded anywhere near peak frequency. In fact, we aren't doing anything multithreaded past those terrible 2.7GHz base clocks at best. Meanwhile, the M2 TDP didn't really increase. They can hit 3.5GHz on 4 cores while using 60% less energy than those AMD cores at 3.7GHz despite being about twice as wide and over 60% faster per clock. Back of the envelope calculations seem to indicate that 4 M2 big cores at 3.5GHz should be more than 2x as fast as 8 Zen 3 cores at 2.7GHz without even using little cores and completely ignoring Amdahl's Law. Of course, all this just goes back to the question of how questionable this entire article really is.

by hajile 4y ago

kllrnohj 4y ago

[citation needed]

mkopec 4y ago

That's Intel's boost behavior, AMD is much more linear. My 4750U in performance mode never exceeds 25W and settles at 23W under sustained load.

hajile 4y ago
What device is that chip in and at what frequencies is it running (by number of cores in use)?
- mkopec 4y ago
  Lenovo ThinkPad Gen1 AMD, Arch Linux, acpi platform_profile = performance When running stress-ng, measured with turbostat: - 4.18 GHz single thread consuming 9W - 3 GHz 16 threads consuming 25W, ramping down to 2.94 / 23W after a couple of seconds and when compiling Linux on 16 threads it stays at 2.85 GHz / 23W In performance mode it does run at 80 degC under sustained load, so usually when undocked I just leave it in balanced mode where it's capped at 20W short / 15W long Also worth noting is that in low-power mode (11W / 11W) it'll still hit max single core frequency possible.

bnieuwen 4y ago

Actually Phoronix has power benchmarks for the ACPI power profiles[1]. Seems like a boost to ~28W or so with a long term average of 22-23W. (Note that this is SoC package power instead of the full laptop though, but that is pretty typical, so no idea what the 22W was for comparison.) [1] https://www.phoronix.com/review/ryzen7-6850u-acpi https://www.phoronix.com/review/ryzen7-6850u-acpi

hajile 4y ago
I don't believe those numbers. The 4800U hit north of 65w in a NUC device[0]. The 5800U hits 52w in a laptop[1]. AMD runs their chips hot. TSMC N6 is a 7nm++ node. The even more advanced 5nm node only offers either 15% performance increase OR 30% power reduction vs N7. The 6850 clocks 10% higher, so the power shouldn't be dropping AT ALL. The 6850H has an identical turbo clockspeed of 4.7GHz and a TDP of 45w with real-world power consumption according to other reviewers being north of 65w. The base clocks for these chips is 2.7 and 3.5GHz respectively. In the case that they really are getting those numbers, they are certainly only at base clockspeeds (2.7GHz) which raises the impossible question of how Zen 3 suddenly got such a huge performance per clock advantage going from desktop to mobile. The numbers simply do not add up. [0] https://www.anandtech.com/show/16236/asrock-4x4-box4800u-renoir-nuc-review/11 https://www.anandtech.com/show/16236/asrock-4x4-box4800u-ren... [1] https://www.notebookcheck.net/R7-5800U-vs-E-2186M-vs-R7-PRO-5875U_12976_9902_14365.247596.0.html https://www.notebookcheck.net/R7-5800U-vs-E-2186M-vs-R7-PRO-...
- wmf 4y ago
  Firmware can set the power limit to whatever it wants. With the exact same processor, one computer may hit 65 W while a different one is limited to 28 W. There's also huge diminishing utility when it comes to power, so it's possible that the chip is only slightly slower at 28 W than at higher power.
  - hajile 4y ago
    That diminishing return is much more true at 150w than at 50w. https://www.anandtech.com/show/16214/amd-zen-3-ryzen-deep-dive-review-5950x-5900x-5800x-and-5700x-tested/8 https://www.anandtech.com/show/16214/amd-zen-3-ryzen-deep-di... When you look at per-core performance of desktop chips, things aren't rosy. Looking at the 5950 (most power efficient per core), it's taking almost 7.5w PER CORE to hit 3.7GHz. It hits 4.7GHz (peak frequency of 6850U) on just 4 cores while using 110w to do it. That's almost 23w per core. Based on these numbers, taking 8 cores up to 3.7GHz would require 60w of power and that's just to hit the "base" frequencies of the 6850H which they say can be done with a TDP 25% lower than that (maybe dropping half the L3 cache makes that possible, but at an overall performance loss as moving stuff from RAM takes more energy than keeping it in L3 and I don't know that losing half the cache saves more energy than the addition of a GPU adds back to the chip). Even if we assume a 12% energy efficiency bump (two thirds of the 18% transistor reduction and roughly inline with the 30% efficiency at N5 with a 45% transistor reduction), we aren't doing anything multithreaded anywhere near peak frequency. In fact, we aren't doing anything multithreaded past those terrible 2.7GHz base clocks at best. Meanwhile, the M2 TDP didn't really increase. They can hit 3.5GHz on 4 cores while using 60% less energy than those AMD cores at 3.7GHz despite being about twice as wide and over 60% faster per clock. Back of the envelope calculations seem to indicate that 4 M2 big cores at 3.5GHz should be more than 2x as fast as 8 Zen 3 cores at 2.7GHz without even using little cores and completely ignoring Amdahl's Law. Of course, all this just goes back to the question of how questionable this entire article really is.