Re: [RFC 00/11] uprobes: Add support to optimize usdt probes on x86_64

[Peter Zijlstra]

On Tue, Nov 05, 2024 at 02:33:54PM +0100, Jiri Olsa wrote:
> hi,
> this patchset adds support to optimize usdt probes on top of 5-byte
> nop instruction.
> 
> The generic approach (optimize all uprobes) is hard due to emulating
> possible multiple original instructions and its related issues. The
> usdt case, which stores 5-byte nop seems much easier, so starting
> with that.
> 
> The basic idea is to replace breakpoint exception with syscall which
> is faster on x86_64. For more details please see changelog of patch 7.

So this is really about the fact that syscalls are faster than traps on
x86_64? Is there something similar on ARM64, or are they roughly the
same speed there?

That is, I don't think this scheme will work for the various RISC
architectures, given their very limited immediate range turns a typical
call into a multi-instruction trainwreck real quick.

Now, that isn't a problem if their exceptions and syscalls are of equal
speed.