Re: [PATCH v8 0/7] Optimize dm-verity and fsverity using multibuffer hashing

[Eric Biggers]

On Sun, Feb 16, 2025 at 10:27:02AM +0800, Herbert Xu wrote:
> On Sat, Feb 15, 2025 at 09:04:12AM -0800, Jakub Kicinski wrote:
> >
> > Can confirm, FWIW. I don't know as much about IPsec, but for TLS
> > lightweight SW-only crypto would be ideal.
> 
> Please note that while CPU-only crypto is the best for networking,
> it actually operates in asynchronous mode on x86.  This is because
> RX occurs in softirq context, which may not be able to use SIMD on
> x86.

Well, the async fallback (using cryptd) occurs only when a kernel-mode FPU
section in process context is interrupted by a hardirq and at the end of it a
softirq also tries to use kernel-mode FPU.  It's generally a rare case but also
a terrible implementation that is really bad for performance; this should never
have been implemented this way.  I am planning to fix it so that softirqs on x86
will always be able to use the FPU, like they can on some of the other arches
like arm64 and riscv.

- Eric