[resending as I somehow messed up the 'From' header and got a tonne of
bounces]

On Thu, Nov 21, 2024 at 08:47:56AM -0800, Alexei Starovoitov wrote:

On Thu, Nov 21, 2024 at 8:34 AM Peter Zijlstra [off-list ref] wrote:

quoted

Elsewhere in the thread Mark Rutland already noted that arm64 really
doesn't need or want this.

Doesn't look like you've read what you quoted above.
On arm64 the _HW_ cost may be the same.
The _SW_ difference in handling trap vs syscall is real.
I bet once uprobe syscall is benchmarked on arm64 there will
be a delta.

I already pointed out in [1] that on arm64 we can make the trap case
*faster* than the syscall. If that's not already the case, there's only
a small amount of rework needed, (pulling BRK handling into
entry-common.c), which we want to do for other reasons anyway.

On arm64 I do not want the syscall; the trap is faster and simpler to
maintain.

Mark

[1] https://lore.kernel.org/lkml/ZzsRfhGSYXVK0mst@J2N7QTR9R3/ (local)