From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753228AbbF0Iwk (ORCPT ); Sat, 27 Jun 2015 04:52:40 -0400 Received: from mail9.hitachi.co.jp ([133.145.228.44]:57836 "EHLO mail9.hitachi.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753078AbbF0Iwc (ORCPT ); Sat, 27 Jun 2015 04:52:32 -0400 Message-ID: <558E6449.8080103@hitachi.com> Date: Sat, 27 Jun 2015 17:52:25 +0900 From: Masami Hiramatsu Organization: Hitachi, Ltd., Japan User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0 MIME-Version: 1.0 To: He Kuang , ast@plumgrid.com, rostedt@goodmis.org, mingo@redhat.com, acme@redhat.com CC: wangnan0@huawei.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH] bpf: Put perf_events check ahead of bpf prog References: <1435387495-141813-1-git-send-email-hekuang@huawei.com> In-Reply-To: <1435387495-141813-1-git-send-email-hekuang@huawei.com> Content-Type: text/plain; charset=iso-2022-jp Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2015/06/27 15:44, He Kuang wrote: > When we add a kprobe point and record events by perf, the execution path > of all threads on each cpu will enter this point, but perf may only > record events on a particular thread or cpu at this kprobe point, a > check on call->perf_events list filters out the threads which perf is > not recording. > > Currently, bpf_prog will be entered at the beginning of > kprobe_perf_func() before the above check, which makes bpf_prog be > executed in every threads including determined not to be recorded > threads. A simple test can demonstrate this: > > 'bpf_prog_on_write.o' contains a bpf prog which outputs to trace buffer > when it is entered. Run a background thread 'another-dd' and 'dd' > simultaneously, but only record 'dd' thread by perf. The result shows > all threads trigger bpf_prog. > > $ another-dd if=/dev/zero of=test1 bs=4k count=1000000 > $ perf record -v --event bpf_prog_on_write.o -- dd if=/dev/zero of=test2 bs=4k count=3 > $ cat /sys/kernel/debug/tracing/trace > another-dd-1007 [000] d... 120.225835: : generic_perform_write: tgid=1007, pid=1007 > another-dd-1007 [000] d... 120.227123: : generic_perform_write: tgid=1007, pid=1007 > [repeat many times...] > another-dd-1007 [000] d... 120.412395: : generic_perform_write: tgid=1007, pid=1007 > another-dd-1007 [000] d... 120.412524: : generic_perform_write: tgid=1007, pid=1007 > dd-1009 [000] d... 120.413080: : generic_perform_write: tgid=1009, pid=1009 > dd-1009 [000] d... 120.414846: : generic_perform_write: tgid=1009, pid=1009 > dd-1009 [000] d... 120.415013: : generic_perform_write: tgid=1009, pid=1009 > another-dd-1007 [000] d... 120.416128: : generic_perform_write: tgid=1007, pid=1007 > another-dd-1007 [000] d... 120.416295: : generic_perform_write: tgid=1007, pid=1007 > > This patch moves the check on perf_events list ahead and skip running > bpf_prog on threads perf not care. > > After this patch: > > $ another-dd if=/dev/zero of=test1 bs=4k count=1000000 > $ perf record -v --event bpf_prog_on_write.o -- dd if=/dev/zero of=test2 bs=4k count=3 > $ cat /sys/kernel/debug/tracing/trace > dd-994 [000] d... 46.386754: : generic_perform_write: tgid=994, pid=994 > dd-994 [000] d... 46.389167: : generic_perform_write: tgid=994, pid=994 > dd-994 [000] d... 46.389551: : generic_perform_write: tgid=994, pid=994 This looks nice :) Acked-by: Masami Hiramatsu Thank you! > > Signed-off-by: He Kuang > --- > kernel/trace/trace_kprobe.c | 12 ++++++------ > 1 file changed, 6 insertions(+), 6 deletions(-) > > diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c > index d0ce590..5600df8 100644 > --- a/kernel/trace/trace_kprobe.c > +++ b/kernel/trace/trace_kprobe.c > @@ -1141,13 +1141,13 @@ kprobe_perf_func(struct trace_kprobe *tk, struct pt_regs *regs) > int size, __size, dsize; > int rctx; > > - if (prog && !trace_call_bpf(prog, regs)) > - return; > - > head = this_cpu_ptr(call->perf_events); > if (hlist_empty(head)) > return; > > + if (prog && !trace_call_bpf(prog, regs)) > + return; > + > dsize = __get_data_size(&tk->tp, regs); > __size = sizeof(*entry) + tk->tp.size + dsize; > size = ALIGN(__size + sizeof(u32), sizeof(u64)); > @@ -1176,13 +1176,13 @@ kretprobe_perf_func(struct trace_kprobe *tk, struct kretprobe_instance *ri, > int size, __size, dsize; > int rctx; > > - if (prog && !trace_call_bpf(prog, regs)) > - return; > - > head = this_cpu_ptr(call->perf_events); > if (hlist_empty(head)) > return; > > + if (prog && !trace_call_bpf(prog, regs)) > + return; > + > dsize = __get_data_size(&tk->tp, regs); > __size = sizeof(*entry) + tk->tp.size + dsize; > size = ALIGN(__size + sizeof(u32), sizeof(u64)); > -- Masami HIRAMATSU Linux Technology Research Center, System Productivity Research Dept. Center for Technology Innovation - Systems Engineering Hitachi, Ltd., Research & Development Group E-mail: masami.hiramatsu.pt@hitachi.com