On Wed, Feb 19, 2025 at 09:13:23PM -0800, Eric Biggers wrote: > The patchset can also be retrieved from: > > git fetch https://git.kernel.org/pub/scm/linux/kernel/git/ebiggers/linux.git x86-softirq-fpu-fix-v1 > > This patchset fixes a longstanding issue where kernel-mode FPU (i.e., > SIMD) was not reliably usable in softirqs in x86, which was creating the > need for a fallback. The fallback was really bad for performance, and > it even hurt performance for users that never encountered the edge case > where kernel-mode FPU was not usable. > > This patchset aligns x86 with other architectures such as arm, arm64, > and riscv by making kernel-mode FPU work in softirqs reliably. There > are a few possible ways to achieve that, and for now I just went with > the simplest way; see patch 1 for details. > > Patch 2 eliminates all uses of the "crypto SIMD helper" from x86, as > patch 1 makes it unnecessary. For the RFC it is just one big patch; > I'll probably split patch 2 up if this progresses past RFC status. > > Performance results have been positive. All en/decryption is now > slightly faster on x86, as it no longer take a detour through > crypto/simd.c. I get a 7% or 23% improvement for AES-XTS, for example. > > I also benchmarked bidirectional IPsec, which has been claimed to often > hit the edge case where kernel-mode FPU was previously not usable in > softirq context. Ultimately, I was not actually able to reproduce that > edge case being reached unless I reduced the number of CPUs to 1, in > which case it then started being occasionally reached. Regardless, even > without that case being reached, IPsec throughput still improved by 2%. > In situations where that case was being reached, or where users required > a synchronous algorithm, a much larger improvement should be seen. > > Eric Biggers (2): > x86/fpu: make kernel-mode FPU reliably usable in softirqs > crypto: x86 - stop using the SIMD helper Any thoughts on this from the x86 folks? - Eric
