On Thu, Feb 29, 2024 at 6:39 AM Jiri Olsa <olsajiri@xxxxxxxxx> wrote: > > One of uprobe pain points is having slow execution that involves > two traps in worst case scenario or single trap if the original > instruction can be emulated. For return uprobes there's one extra > trap on top of that. > > My current idea on how to make this faster is to follow the optimized > kprobes and replace the normal uprobe trap instruction with jump to > user space trampoline that: > > - executes syscall to call uprobe consumers callbacks Did you get a chance to measure relative performance of syscall vs int3 interrupt handling? If not, do you think you'll be able to get some numbers by the time the conference starts? This should inform the decision whether it even makes sense to go through all the trouble. > - executes original instructions > - jumps back to continue with the original code > > There are of course corner cases where above will have trouble or > won't work completely, like: > > - executing original instructions in the trampoline is tricky wrt > rip relative addressing > > - some instructions we can't move to trampoline at all > > - the uprobe address is on page boundary so the jump instruction to > trampoline would span across 2 pages, hence the page replace won't > be atomic, which might cause issues > > - ... ? many others I'm sure > > Still with all the limitations I think we could be able to speed up > some amount of the uprobes, which seems worth doing. > > I'd like to have the discussion on the topic and get some agreement > or directions on how this should be done.
