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| author | Pavel Begunkov <asml.silence@gmail.com> | 2023-08-25 00:53:23 +0200 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2023-08-25 01:16:19 +0200 |
| commit | a0727c738309a06ef5579c1742f8f0def63aa883 (patch) | |
| tree | 2733d843c0313e5259bbb8948f5e14ace262d729 /io_uring | |
| parent | io_uring/rsrc: Annotate struct io_mapped_ubuf with __counted_by (diff) | |
| download | linux-a0727c738309a06ef5579c1742f8f0def63aa883.tar.xz linux-a0727c738309a06ef5579c1742f8f0def63aa883.zip | |
io_uring: improve cqe !tracing hot path
While looking at io_fill_cqe_req()'s asm I stumbled on our trace points
turning into the chunk below:
trace_io_uring_complete(req->ctx, req, req->cqe.user_data,
req->cqe.res, req->cqe.flags,
req->extra1, req->extra2);
io_uring/io_uring.c:898: trace_io_uring_complete(req->ctx, req, req->cqe.user_data,
movq 232(%rbx), %rdi # req_44(D)->big_cqe.extra2, _5
movq 224(%rbx), %rdx # req_44(D)->big_cqe.extra1, _6
movl 84(%rbx), %r9d # req_44(D)->cqe.D.81184.flags, _7
movl 80(%rbx), %r8d # req_44(D)->cqe.res, _8
movq 72(%rbx), %rcx # req_44(D)->cqe.user_data, _9
movq 88(%rbx), %rsi # req_44(D)->ctx, _10
./arch/x86/include/asm/jump_label.h:27: asm_volatile_goto("1:"
1:jmp .L1772 # objtool NOPs this #
...
It does a jump_label for actual tracing, but those 6 moves will stay
there in the hottest io_uring path. As an optimisation, add a
trace_io_uring_complete_enabled() check, which is also uses jump_labels,
it tricks the compiler into behaving. It removes the junk without
changing anything else int the hot path.
Note: apparently, it's not only me noticing it, and people are also
working it around. We should remove the check when it's solved
generically or rework tracing.
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/555d8312644b3776f4be7e23f9b92943875c4bc7.1692916914.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'io_uring')
| -rw-r--r-- | io_uring/io_uring.h | 9 |
1 files changed, 5 insertions, 4 deletions
diff --git a/io_uring/io_uring.h b/io_uring/io_uring.h index 3e6ff3cd9a24..465598223386 100644 --- a/io_uring/io_uring.h +++ b/io_uring/io_uring.h @@ -145,10 +145,11 @@ static inline bool io_fill_cqe_req(struct io_ring_ctx *ctx, struct io_kiocb *req if (unlikely(!cqe)) return false; - trace_io_uring_complete(req->ctx, req, req->cqe.user_data, - req->cqe.res, req->cqe.flags, - (req->flags & REQ_F_CQE32_INIT) ? req->extra1 : 0, - (req->flags & REQ_F_CQE32_INIT) ? req->extra2 : 0); + if (trace_io_uring_complete_enabled()) + trace_io_uring_complete(req->ctx, req, req->cqe.user_data, + req->cqe.res, req->cqe.flags, + (req->flags & REQ_F_CQE32_INIT) ? req->extra1 : 0, + (req->flags & REQ_F_CQE32_INIT) ? req->extra2 : 0); memcpy(cqe, &req->cqe, sizeof(*cqe)); |