[Gate-users] Report - Investigating Intel Meltdown/Spectre patches and Ryzen hyperthreading benchmarks

[David Boersma]

Hi Bryan,


Thanks for sharing this report with us! It reminds me that we should update/upgrade that guidance (about number of cores to use) a bit on the wiki.


I see that in your test you tried to make the benchmark use case as CPU-dominated as possible. In my very crude understanding of hyperthreading (a core pretends to be two cores by switching very quickly between two processes), this kind of guarantees your conclusion (1); hyperthreading is mostly useful for jobs in which for a single instance the CPU is waiting for other resources about half of the time, because then with many instances instead of waiting a core can do CPU-work for some other instance. So if you add back all the IO-intensive tasks, it may turn out that hyperthreading actually does help a bit to increase efficiency. (This might be out of scope for your report.)


You write at the top of your report that it was "published" on November 19. Did it get published elsewhere, e.g. on a website or magazine or forum (other than gate-users), or do you just mean that you saved it publicly readable on OneDrive?


Best regards,

David Boersma

________________________________
Von: Gate-users <gate-users-bounces at lists.opengatecollaboration.org> im Auftrag von Bryan McIntosh <mcintoshster at gmail.com>
Gesendet: Dienstag, 20. November 2018 05:12:50
An: gate-users at lists.opengatecollaboration.org
Betreff: [Gate-users] Report - Investigating Intel Meltdown/Spectre patches and Ryzen hyperthreading benchmarks

Hi everyone,

I've been using GATE for a while, and one thing that has been a bit lacking in our community is benchmarks for various CPU architectures. When the patches for the Meltdown and Spectre vulnerabilities were revealed to reduce performance quite substantially in some applications, I wondered how GATE and Geant4 would be affected by installing them on an older Intel CPU that is missing some of the alternate instructions used to mitigate some of the slowdowns. I also was frustrated that no one had released any data on how well AMD Ryzen CPUs perform in GATE, so I ran a series of benchmarks investigating the following questions:

1) How does memory speed affect the performance of second-generation AMD Ryzen CPUs?

2) Does the hyperthreading offered on Ryzen CPUs and some higher-end Intel CPUs provide any performance benefit for GATE? Previous guidance on this was that it did not, but that was written years ago with different CPU architectures on the market.

3) How much performance impact do the Meltdown/Spectre patches have on GATE simulation times on older (ie. second and third generation Core i5 and Core i7) Intel CPUs?

I've written my results in a report that is available for download at https://1drv.ms/b/s!Al3r4ajL5Z4jkLs7LVyGSI_MmA-uzg. Any comments or questions you have would be welcome, and if anyone is interested in running the same benchmark scripts on their GATE installation I would be glad to upload them for testing.

Best regards,

-Bryan McIntosh
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