Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754452AbbFSN5s (ORCPT ); Fri, 19 Jun 2015 09:57:48 -0400 Received: from mail.bmw-carit.de ([62.245.222.98]:49492 "EHLO linuxmail.bmw-carit.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751883AbbFSN5j (ORCPT ); Fri, 19 Jun 2015 09:57:39 -0400 From: Daniel Wagner To: Alexei Starovoitov Cc: Daniel Wagner , "David S. Miller" , Daniel Borkmann , Ingo Molnar , linux-kernel@vger.kernel.org, netdev@vger.kernel.org Subject: [PATCH v1] bpf: BPF based latency tracing Date: Fri, 19 Jun 2015 15:57:27 +0200 Message-Id: <1434722247-9952-1-git-send-email-daniel.wagner@bmw-carit.de> X-Mailer: git-send-email 2.1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 8924 Lines: 176 BPF offers another way to generate latency histograms. We attach kprobes at trace_preempt_off and trace_preempt_on and calculate the time it takes to from seeing the off/on transition. The first array is used to store the start time stamp. The key is the CPU id. The second array stores the log2(time diff). We need to use static allocation here (array and not hash tables). The kprobes hooking into trace_preempt_on|off should not calling any dynamic memory allocation or free path. We need to avoid recursivly getting called. Besides that, it reduces jitter in the measurement. CPU 0 latency : count distribution 1 -> 1 : 0 | | 2 -> 3 : 0 | | 4 -> 7 : 0 | | 8 -> 15 : 0 | | 16 -> 31 : 0 | | 32 -> 63 : 0 | | 64 -> 127 : 0 | | 128 -> 255 : 0 | | 256 -> 511 : 0 | | 512 -> 1023 : 0 | | 1024 -> 2047 : 0 | | 2048 -> 4095 : 166723 |*************************************** | 4096 -> 8191 : 19870 |*** | 8192 -> 16383 : 6324 | | 16384 -> 32767 : 1098 | | 32768 -> 65535 : 190 | | 65536 -> 131071 : 179 | | 131072 -> 262143 : 18 | | 262144 -> 524287 : 4 | | 524288 -> 1048575 : 1363 | | CPU 1 latency : count distribution 1 -> 1 : 0 | | 2 -> 3 : 0 | | 4 -> 7 : 0 | | 8 -> 15 : 0 | | 16 -> 31 : 0 | | 32 -> 63 : 0 | | 64 -> 127 : 0 | | 128 -> 255 : 0 | | 256 -> 511 : 0 | | 512 -> 1023 : 0 | | 1024 -> 2047 : 0 | | 2048 -> 4095 : 114042 |*************************************** | 4096 -> 8191 : 9587 |** | 8192 -> 16383 : 4140 | | 16384 -> 32767 : 673 | | 32768 -> 65535 : 179 | | 65536 -> 131071 : 29 | | 131072 -> 262143 : 4 | | 262144 -> 524287 : 1 | | 524288 -> 1048575 : 364 | | CPU 2 latency : count distribution 1 -> 1 : 0 | | 2 -> 3 : 0 | | 4 -> 7 : 0 | | 8 -> 15 : 0 | | 16 -> 31 : 0 | | 32 -> 63 : 0 | | 64 -> 127 : 0 | | 128 -> 255 : 0 | | 256 -> 511 : 0 | | 512 -> 1023 : 0 | | 1024 -> 2047 : 0 | | 2048 -> 4095 : 40147 |*************************************** | 4096 -> 8191 : 2300 |* | 8192 -> 16383 : 828 | | 16384 -> 32767 : 178 | | 32768 -> 65535 : 59 | | 65536 -> 131071 : 2 | | 131072 -> 262143 : 0 | | 262144 -> 524287 : 1 | | 524288 -> 1048575 : 174 | | CPU 3 latency : count distribution 1 -> 1 : 0 | | 2 -> 3 : 0 | | 4 -> 7 : 0 | | 8 -> 15 : 0 | | 16 -> 31 : 0 | | 32 -> 63 : 0 | | 64 -> 127 : 0 | | 128 -> 255 : 0 | | 256 -> 511 : 0 | | 512 -> 1023 : 0 | | 1024 -> 2047 : 0 | | 2048 -> 4095 : 29626 |*************************************** | 4096 -> 8191 : 2704 |** | 8192 -> 16383 : 1090 | | 16384 -> 32767 : 160 | | 32768 -> 65535 : 72 | | 65536 -> 131071 : 32 | | 131072 -> 262143 : 26 | | 262144 -> 524287 : 12 | | 524288 -> 1048575 : 298 | | All this is based on the trace3 examples written by Alexei Starovoitov . Signed-off-by: Daniel Wagner Cc: Alexei Starovoitov Cc: "David S. Miller" Cc: Daniel Borkmann Cc: Ingo Molnar Cc: linux-kernel@vger.kernel.org Cc: netdev@vger.kernel.org --- Hi Alexei, Something broke in my toolchain and it took me a while to figure out whats going on. With the rebase on net-next no additinal patches are needed and this thing here runs fine. cheers, daniel changes v1: - rebases on net-next v0: - renamed to lathist since there is no direct hw latency involved - use arrays instead of hash tables samples/bpf/Makefile | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile index 46c6a8c..4450fed 100644 --- a/samples/bpf/Makefile +++ b/samples/bpf/Makefile @@ -12,6 +12,7 @@ hostprogs-y += tracex2 hostprogs-y += tracex3 hostprogs-y += tracex4 hostprogs-y += tracex5 +hostprogs-y += lathist test_verifier-objs := test_verifier.o libbpf.o test_maps-objs := test_maps.o libbpf.o @@ -24,6 +25,7 @@ tracex2-objs := bpf_load.o libbpf.o tracex2_user.o tracex3-objs := bpf_load.o libbpf.o tracex3_user.o tracex4-objs := bpf_load.o libbpf.o tracex4_user.o tracex5-objs := bpf_load.o libbpf.o tracex5_user.o +lathist-objs := bpf_load.o libbpf.o lathist_user.o # Tell kbuild to always build the programs always := $(hostprogs-y) @@ -36,6 +38,7 @@ always += tracex3_kern.o always += tracex4_kern.o always += tracex5_kern.o always += tcbpf1_kern.o +always += lathist_kern.o HOSTCFLAGS += -I$(objtree)/usr/include @@ -48,6 +51,7 @@ HOSTLOADLIBES_tracex2 += -lelf HOSTLOADLIBES_tracex3 += -lelf HOSTLOADLIBES_tracex4 += -lelf -lrt HOSTLOADLIBES_tracex5 += -lelf +HOSTLOADLIBES_lathist += -lelf # point this to your LLVM backend with bpf support LLC=$(srctree)/tools/bpf/llvm/bld/Debug+Asserts/bin/llc -- 2.1.0 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in Please read the FAQ at http://www.tux.org/lkml/