From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2B6618592A for ; Wed, 20 Mar 2024 20:06:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1710965173; cv=none; b=khe10bCiGCDaACyjEEa94vbVzAOyxO0RjMKrhS705BhTj1aj/XjQ9O+NrDtIimwDuja8lBHt2Xhcq4DKGHpiuCb1AQNpBkq+Dtl3QMyBBwGsJ5VSE/pI3UowQ9swwM3bWxA6Y7GuQRBRSkAGbQ73olHUn7OEHHGA8yT0Dzo0TWA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1710965173; c=relaxed/simple; bh=2phJ7QkwthDNu8T5xsVMkXxbshunQfDBz/hwjFgzEKA=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=lJ/KZWeBF8KqPDtWR8NtbFZY6snEWR7LcVa1voH98OOADId+v3W1t68ulUa0CL6dgrFmWPqzqikSgwwApTcg8APBUSB3UZMV9J3FeGRaHIT79uDMrtx4o6lS3cN46+Yx0IncKcuKjeuADhUuwwUju8t/QKckOHErGwHpD2L4ZnI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=BTM6AAdv; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="BTM6AAdv" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6E3BDC433F1; Wed, 20 Mar 2024 20:06:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1710965172; bh=2phJ7QkwthDNu8T5xsVMkXxbshunQfDBz/hwjFgzEKA=; h=From:To:Cc:Subject:Date:From; b=BTM6AAdv4EXK4kfjtfQ5373fooR1H8ddxJiPrHXqKYk78LgKGISNQAkfoapQ5Xfok raVayfb2aU/RHRDqTvauxaeTIw0YRETYYz+prC7SrOvlmyABD2XCTW72w+FRl6SiHE bJGk1RhBrB+QlW5omY68TrBZTibuymrrL4dpMfyoEq5UgDfRRylBpJG+iS5d0MGAAn w82ZpzRWlpg0n2+oAzU02BjeKtjAVkC7A0LJpursRLpslN/elqN7NrfCeCpXfiK66v 1b+1MRzy/UXUXNNq4sMtYaITlpV+XISkaMu2MceFZgbI1XTPJ5DsXwBFjOsF/HK+8V 8xHfQ3v2b0jxQ== From: Andrii Nakryiko To: bpf@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net, martin.lau@kernel.org Cc: andrii@kernel.org, kernel-team@meta.com Subject: [PATCH bpf-next] bpf: mark kprobe_multi_link_prog_run as always inlined function Date: Wed, 20 Mar 2024 13:06:10 -0700 Message-ID: <20240320200610.2556049-1-andrii@kernel.org> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit kprobe_multi_link_prog_run() is called both for multi-kprobe and multi-kretprobe BPF programs from kprobe_multi_link_handler() and kprobe_multi_link_exit_handler(), respectively. kprobe_multi_link_prog_run() is doing all the relevant work, with those wrappers just satisfying ftrace's interfaces (kprobe callback is supposed to return int, while kretprobe returns void). With this structure compile performs tail-call optimization: Dump of assembler code for function kprobe_multi_link_exit_handler: 0xffffffff8122f1e0 <+0>: add $0xffffffffffffffc0,%rdi 0xffffffff8122f1e4 <+4>: mov %rcx,%rdx 0xffffffff8122f1e7 <+7>: jmp 0xffffffff81230080 This means that when trying to capture LBR that traces all indirect branches we are wasting an entry just to record that kprobe_multi_link_exit_handler called/jumped into kprobe_multi_link_prog_run. LBR entries are especially sparse on AMD CPUs (just 16 entries on latest CPUs vs typically 32 on latest Intel CPUs), and every entry counts (and we already have a bunch of other LBR entries spent getting to a BPF program), so it would be great to not waste any more than necessary. Marking it as just `static inline` doesn't change anything, compiler still performs tail call optimization only. But by marking kprobe_multi_link_prog_run() as __always_inline we ensure that compiler fully inlines it, avoiding jumps: Dump of assembler code for function kprobe_multi_link_exit_handler: 0xffffffff8122f4e0 <+0>: push %r15 0xffffffff8122f4e2 <+2>: push %r14 0xffffffff8122f4e4 <+4>: push %r13 0xffffffff8122f4e6 <+6>: push %r12 0xffffffff8122f4e8 <+8>: push %rbx 0xffffffff8122f4e9 <+9>: sub $0x10,%rsp 0xffffffff8122f4ed <+13>: mov %rdi,%r14 0xffffffff8122f4f0 <+16>: lea -0x40(%rdi),%rax ... 0xffffffff8122f590 <+176>: call 0xffffffff8108e420 0xffffffff8122f595 <+181>: sub %r14,%rax 0xffffffff8122f598 <+184>: add %rax,0x8(%rbx,%r13,1) 0xffffffff8122f59d <+189>: jmp 0xffffffff8122f541 Signed-off-by: Andrii Nakryiko --- kernel/trace/bpf_trace.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c index 434e3ece6688..0bebd6f02e17 100644 --- a/kernel/trace/bpf_trace.c +++ b/kernel/trace/bpf_trace.c @@ -2796,7 +2796,7 @@ static u64 bpf_kprobe_multi_entry_ip(struct bpf_run_ctx *ctx) return run_ctx->entry_ip; } -static int +static __always_inline int kprobe_multi_link_prog_run(struct bpf_kprobe_multi_link *link, unsigned long entry_ip, struct pt_regs *regs) { -- 2.43.0