On Thu, Nov 21, 2024 at 4:17 AM Peter Zijlstra [off-list ref] wrote:

On Wed, Nov 20, 2024 at 04:07:38PM -0800, Andrii Nakryiko wrote:

quoted

USDTs are meant to be "transparent" to the surrounding code and they
don't mark any clobbered registers. Technically it could be added, but
I'm not a fan of this.

Sure. Anyway, another thing to consider is FRED, will all of this still
matter once that lands? If FRED gets us INT3 performance close to what
SYSCALL has, then all this work will go unused.

afaik not a single cpu in the datacenter supports FRED while
uprobe overhead is real.
imo it's worth improving performance today for existing cpus.
I suspect arm64 might benefit too. Even if arm hw does the same
amount of work for trap vs syscall the sw overhead of handling
trap is different.
I suspect that equation will apply to future FRED cpus too.