enable fsgsbase instructions on Linux 5.9+ for EOS VM OC
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spoonincode
commented
Jan 27, 2025
| const char disable_str[] = "SPRING_DISABLE_FSGSBASE"; | ||
| if(strncmp(*my_environ++, disable_str, strlen(disable_str)) == 0) | ||
| return 0; | ||
| } |
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This is the same mess as I used in bls,
AntelopeIO/bls12-381#4 (comment)
Don't really know what to do here. Disabling optimizations via environment variable is nice. Seems hard to believe _dl_argv would ever deviate.
heifner
approved these changes
Jan 27, 2025
greg7mdp
approved these changes
Jan 27, 2025
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Note:start |
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EOS VM OC uses the GS segment register for the base of its WASM memory. Prior to Linux 5.9 the only way to adjust the base address is via a syscall. For 5.9+, combined with modern CPUs (Intel Ivy Bridge+, 2012; AMD Bulldozer+, 2011), it's possible to instead use the
fsgsbaseinstructions from userspace without needing to make a syscall. Switching to these instructions eliminates at least one syscall per action, and oftentimes more for something like EVM.I ran a replay test over blocks 96328736-96627942 on an i7-12700K (Alder Lake, 2021). I saw a surprising ~3.5% improvement. This far exceeds my expectations (should have done this years ago). I was anticipating that only older CPUs subject to Meltdown would incur such heavy overhead on this seemingly simplistic syscall. What might explain this is that Alder Lake is subject to the swapgs spectre variant, but I have not confirmed that is the source of the slow down.
I had planed to dig out an 8th gen Core CPU (with Meltdown) to benchmark with but now I'm not sure I'll go through the trouble since the gains are so impressive on modern gen.
I have created,
https://github.com/AntelopeIO/spring/wiki/Environment-Variables-Controlling-CPU-Features
to track the various environment variables controlling CPU instruction usage.