On 3/5/24 15:53, Song Liu wrote:
On Tue, Mar 5, 2024 at 9:18 AM Jiri Olsa <olsajiri@xxxxxxxxx> wrote:
On Fri, Mar 01, 2024 at 11:39:03AM -0800, Kui-Feng Lee wrote:
On 2/29/24 06:39, Jiri Olsa 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
- 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.
Just a random idea related to this.
Could we also run jit code of bpf programs in the user space to collect
information instead of going back to the kernel every time?
I was thinking about a similar idea. I guess these user space BPF
programs will have limited features that we can probably use them
update bpf maps. For this limited scope, we still need bpf_arena.
Otherwise, the user space bpf program will need to update the bpf
maps with sys_bpf(), which adds the same overhead as triggering
That is true. However, even without bpf_arena, it still works with
some workarounds without going through sys_bpf().
the program with a syscall.
sorry for late reply, do you mean like ubpf? the scope of this change
is to speed up the generic uprobe, ebpf is just one of the consumers
I guess this means we need a new syscall?
Thanks,
Song
