From: Theo Buehler <tb@theobuehler.org>
Subject: Re: VFS syscalls & KERNEL_LOCK()
To: Martin Pieuchot <mpi@grenadille.net>
Cc: tech@openbsd.org
Date: Tue, 3 Dec 2024 06:21:06 +0100

On Thu, Nov 28, 2024 at 07:59:50PM +0100, Martin Pieuchot wrote:
> Diff below pushes the KERNEL_LOCK() inside the following syscalls:
> 
> - open(2) & openat(2)
> - stat(2), lstat(2), fstat(2), fstatat(2)
> - __realpath()
> 
> It makes %sys time decrease by ~5% here on the usual libLLVM parallel
> build.

I ran an amd64 bulk build with this. It may have been a bit faster than
the previous runs (2d 7h 5m vs 2d 7h 30m), but this is less than 1% and
within the usual noise of bulk build times.

It also works seemingly without issues on my daily driver and my mac m1
mini.

> More importantly it shows that doopenat() is the most contended
> "syscall" by far in FlameGraphs.
> 
> Reviews, tests and oks welcome!

I have read the diff and could not spot anything wrong with it, but
it's very far away from my usual stomping grounds. So for whatever
that's worth, I am ok with this going in.