Eric Biggers <ebiggers@xxxxxxxxxx> 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. Great work! > 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. You would need a situation where your CPU is maxed out by your bandwidth, so on a physical box these days you would need 10GbE at the minimum. However, I used to be able to easily reproduce this using virtualisation because there the bandwidth is essentially unlimited. So perhaps a KVM guest with a single CPU doing bidirection IPsec to the host should be enough to reproduce this case. Thanks, -- Email: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx> Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
