On Thu, Dec 15, 2022 at 11:43:22AM +0100, Ard Biesheuvel wrote: > On Thu, 15 Dec 2022 at 11:27, Linus Walleij <linus.walleij@xxxxxxxxxx> wrote: > > > > On Wed, Dec 7, 2022 at 11:39 AM Ard Biesheuvel <ardb@xxxxxxxxxx> wrote: > > > > > We currently only permit kernel mode NEON in process context, to avoid > > > the need to preserve/restore the NEON register file when taking an > > > exception while running in the kernel. > > > > > > Like we did on arm64, we can relax this restriction substantially, by > > > permitting kernel mode NEON from softirq context, while ensuring that > > > softirq processing is disabled when the NEON is being used in task > > > context. This guarantees that only NEON context belonging to user space > > > needs to be preserved and restored, which is already taken care of. > > > > > > This is especially relevant for network encryption, where incoming > > > frames are typically handled in softirq context, and deferring software > > > decryption to a kernel thread or falling back to C code are both > > > undesirable from a performance PoV. > > > > > > Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx> > > > > So boosting WireGuard as primary SW network encryption user? > > Essentially, although the use case that inspired this work is related > to IPsec not WireGuard, and the crypto algorithm in that case (GCM) is > ~3x faster than WG's chacha20poly1305, which makes the performance > overhead of asynchronous completion even more significant. (Note that > GCM needs the AES and PMULL instructions which are usually only > available when running the 32-bit kernel on a 64-bit core, whereas > chacha20poly1305 uses ordinary NEON instructions.) > > But Martin responded with a Tested-by regarding chacha20poly1305 on > IPsec (not WG) where there is also a noticeable speedup, so WG on > ARM32 should definitely benefit from this as well. It'll be interesting to see whether there is any noticable difference with my WG VPN. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!
