3 ms·

What worries me is that those tests are with unpatched kernels. So these drops are only from the microcode updates?!

VMG 9y ago
are the kernel patches accounting for potential microcode fixes?
sp332 9y ago
These firmware updates are for Spectre Variant 2. The kernel patches are for Meltdown (aka Variant 3). So it makes sense to benchmark the changes separately. https://arstechnica.com/gadgets/2018/01/heres-how-and-why-the-spectre-and-meltdown-patches-will-hurt-performance/ https://arstechnica.com/gadgets/2018/01/heres-how-and-why-th... Edit: I'm not sure this is right. RHEL/Centos kernel 3.10.0-693 is vulnerable but 3.10.0-693.11.6 is patched.
- gcbirzan 9y ago
  However, the press release starts with: > Over the past several days, Intel has made further progress to address the exploits known as “Spectre” and “Meltdown.” Then it goes on to say: > Generally speaking, the workloads that incorporate a larger number of user/kernel privilege changes and spend a significant amount of time in privileged mode will be more adversely impacted. All of this implies that they're testing a fixed kernel.
- danieldk 9y ago
  The kernel patches are for Meltdown (aka Variant 3). There are also Spectre fixes landing in kernels. E.g. Linux 4.14.14 added initial retpoline support: https://lwn.net/Articles/744621/ https://lwn.net/Articles/744621/ The current LWN has very good coverage on the latest work on Spectre/Meltdown mitigation in the kernel: https://lwn.net/SubscriberLink/744287/d868ef1ac3f68d70/ https://lwn.net/SubscriberLink/744287/d868ef1ac3f68d70/ (Posting a subscriber link in good faith. If you like such content, please subscribe to LWN.net, they are excellent!)
  - gcbirzan 9y ago
    > There are also Spectre fixes landing in kernels. E.g. Linux 4.14.14 added initial retpoline support: Which has its own performance drawbacks, but the microcode update itself has even more. And you need the microcode update for Broadwell and newer for retpolines to work.
    - sp332 9y ago
      I thought the retpoline basically defeated speculation for certain longjmp/function calls. Why do you need a firmware update for that to work?
      - gcbirzan 9y ago
        That subscriber link above explains why, but in the whitepaper I read, it said Broadwell, not only Skylake.

VMG 9y ago

are the kernel patches accounting for potential microcode fixes?

These firmware updates are for Spectre Variant 2. The kernel patches are for Meltdown (aka Variant 3). So it makes sense to benchmark the changes separately. https://arstechnica.com/gadgets/2018/01/heres-how-and-why-the-spectre-and-meltdown-patches-will-hurt-performance/ https://arstechnica.com/gadgets/2018/01/heres-how-and-why-th... Edit: I'm not sure this is right. RHEL/Centos kernel 3.10.0-693 is vulnerable but 3.10.0-693.11.6 is patched.

gcbirzan 9y ago
However, the press release starts with: > Over the past several days, Intel has made further progress to address the exploits known as “Spectre” and “Meltdown.” Then it goes on to say: > Generally speaking, the workloads that incorporate a larger number of user/kernel privilege changes and spend a significant amount of time in privileged mode will be more adversely impacted. All of this implies that they're testing a fixed kernel.
danieldk 9y ago
The kernel patches are for Meltdown (aka Variant 3). There are also Spectre fixes landing in kernels. E.g. Linux 4.14.14 added initial retpoline support: https://lwn.net/Articles/744621/ https://lwn.net/Articles/744621/ The current LWN has very good coverage on the latest work on Spectre/Meltdown mitigation in the kernel: https://lwn.net/SubscriberLink/744287/d868ef1ac3f68d70/ https://lwn.net/SubscriberLink/744287/d868ef1ac3f68d70/ (Posting a subscriber link in good faith. If you like such content, please subscribe to LWN.net, they are excellent!)
- gcbirzan 9y ago
  > There are also Spectre fixes landing in kernels. E.g. Linux 4.14.14 added initial retpoline support: Which has its own performance drawbacks, but the microcode update itself has even more. And you need the microcode update for Broadwell and newer for retpolines to work.
  - sp332 9y ago
    I thought the retpoline basically defeated speculation for certain longjmp/function calls. Why do you need a firmware update for that to work?
    - gcbirzan 9y ago
      That subscriber link above explains why, but in the whitepaper I read, it said Broadwell, not only Skylake.