On Thu, Nov 21, 2024 at 08:02:12AM -0800, Alexei Starovoitov wrote: > On Thu, Nov 21, 2024 at 4:17 AM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > > > > On Wed, Nov 20, 2024 at 04:07:38PM -0800, Andrii Nakryiko wrote: > > > > > 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 understand, but OTOH adding a syscall now, that we'll have to maintain for years and years, even through we know it'll not be used much is a bit annoying. > 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. Well, the RISC CPUs have a much harder time using this, their immediate range is typically puny and they end up needing multiple instructions and some register in order to set up a call. Elsewhere in the thread Mark Rutland already noted that arm64 really doesn't need or want this.
