| Message ID | 1434722444-10200-1-git-send-email-daniel.wagner@bmw-carit.de |
|---|---|
| State | Accepted, archived |
| Delegated to: | David Miller |
| Headers | show |
On 6/19/15 7:00 AM, Daniel Wagner wrote: > 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. ... > Signed-off-by: Daniel Wagner <daniel.wagner@bmw-carit.de> ... > With the rebase on net-next no additinal patches are needed and this > thing here runs fine. ... > samples/bpf/Makefile | 4 ++ > samples/bpf/lathist_kern.c | 99 +++++++++++++++++++++++++++++++++++++++++++ > samples/bpf/lathist_user.c | 103 +++++++++++++++++++++++++++++++++++++++++++++ > 3 files changed, 206 insertions(+) > create mode 100644 samples/bpf/lathist_kern.c > create mode 100644 samples/bpf/lathist_user.c Thanks. That's a useful example. Acked-by: Alexei Starovoitov <ast@plumgrid.com> Dave, this patch is for net-next and I hope it's not too late for this merge window. -- To unsubscribe from this list: send the line "unsubscribe netdev" in
On 06/19/2015 04:00 PM, Daniel Wagner wrote: > 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 <ast@plumgrid.com>. > > Signed-off-by: Daniel Wagner <daniel.wagner@bmw-carit.de> I think it would be useful to perhaps have two options: 1) User specifies a specific CPU and gets one such an output above. 2) Summary view, i.e. to have the samples of each CPU for comparison next to each other in columns and maybe the histogram view a bit more compressed (perhaps summary of all CPUs). Anyway, it's sample code people can go with and modify individually. Acked-by: Daniel Borkmann <daniel@iogearbox.net> -- To unsubscribe from this list: send the line "unsubscribe netdev" in
On 06/20/2015 10:14 AM, Daniel Borkmann wrote: > I think it would be useful to perhaps have two options: > > 1) User specifies a specific CPU and gets one such an output above. Good point. Will do. > 2) Summary view, i.e. to have the samples of each CPU for comparison > next to each other in columns and maybe the histogram view a bit > more compressed (perhaps summary of all CPUs). I agree, the current view is not really optimal. I'll look into this as well. Alexei indicated that he is working on per-cpu variables support. I think that would be extremely useful to drop the hard coded limit of CPUs and turning this sample code into some more generic code. > Anyway, it's sample code people can go with and modify individually. I am interested to turn this code into a more useful tool. Though I think I miss some background information why this code is kept as samples. Obviously, there is the API and ARCH dependency. As long as an API change can reliable be detected I don't see a real show stopper. Maybe I am too naive. Furthermore I expected that trace_preempt_[on|off] wont change that often. > Acked-by: Daniel Borkmann <daniel@iogearbox.net> Thanks, Daniel -- To unsubscribe from this list: send the line "unsubscribe netdev" in
From: Alexei Starovoitov <ast@plumgrid.com> Date: Fri, 19 Jun 2015 17:53:57 -0700 > On 6/19/15 7:00 AM, Daniel Wagner wrote: >> 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. > ... >> Signed-off-by: Daniel Wagner <daniel.wagner@bmw-carit.de> > ... >> With the rebase on net-next no additinal patches are needed and this >> thing here runs fine. > ... >> samples/bpf/Makefile | 4 ++ >> samples/bpf/lathist_kern.c | 99 >> +++++++++++++++++++++++++++++++++++++++++++ >> samples/bpf/lathist_user.c | 103 >> +++++++++++++++++++++++++++++++++++++++++++++ >> 3 files changed, 206 insertions(+) >> create mode 100644 samples/bpf/lathist_kern.c >> create mode 100644 samples/bpf/lathist_user.c > > Thanks. That's a useful example. > Acked-by: Alexei Starovoitov <ast@plumgrid.com> Applied, thanks. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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 diff --git a/samples/bpf/lathist_kern.c b/samples/bpf/lathist_kern.c new file mode 100644 index 0000000..18fa088 --- /dev/null +++ b/samples/bpf/lathist_kern.c @@ -0,0 +1,99 @@ +/* Copyright (c) 2013-2015 PLUMgrid, http://plumgrid.com + * Copyright (c) 2015 BMW Car IT GmbH + * + * This program is free software; you can redistribute it and/or + * modify it under the terms of version 2 of the GNU General Public + * License as published by the Free Software Foundation. + */ +#include <linux/version.h> +#include <linux/ptrace.h> +#include <uapi/linux/bpf.h> +#include "bpf_helpers.h" + +#define MAX_ENTRIES 20 +#define MAX_CPU 4 + +/* We need to stick to static allocated memory (an array instead of + * hash table) because managing dynamic memory from the + * trace_preempt_[on|off] tracepoints hooks is not supported. + */ + +struct bpf_map_def SEC("maps") my_map = { + .type = BPF_MAP_TYPE_ARRAY, + .key_size = sizeof(int), + .value_size = sizeof(u64), + .max_entries = MAX_CPU, +}; + +SEC("kprobe/trace_preempt_off") +int bpf_prog1(struct pt_regs *ctx) +{ + int cpu = bpf_get_smp_processor_id(); + u64 *ts = bpf_map_lookup_elem(&my_map, &cpu); + + if (ts) + *ts = bpf_ktime_get_ns(); + + return 0; +} + +static unsigned int log2(unsigned int v) +{ + unsigned int r; + unsigned int shift; + + r = (v > 0xFFFF) << 4; v >>= r; + shift = (v > 0xFF) << 3; v >>= shift; r |= shift; + shift = (v > 0xF) << 2; v >>= shift; r |= shift; + shift = (v > 0x3) << 1; v >>= shift; r |= shift; + r |= (v >> 1); + + return r; +} + +static unsigned int log2l(unsigned long v) +{ + unsigned int hi = v >> 32; + + if (hi) + return log2(hi) + 32; + else + return log2(v); +} + +struct bpf_map_def SEC("maps") my_lat = { + .type = BPF_MAP_TYPE_ARRAY, + .key_size = sizeof(int), + .value_size = sizeof(long), + .max_entries = MAX_CPU * MAX_ENTRIES, +}; + +SEC("kprobe/trace_preempt_on") +int bpf_prog2(struct pt_regs *ctx) +{ + u64 *ts, cur_ts, delta; + int key, cpu; + long *val; + + cpu = bpf_get_smp_processor_id(); + ts = bpf_map_lookup_elem(&my_map, &cpu); + if (!ts) + return 0; + + cur_ts = bpf_ktime_get_ns(); + delta = log2l(cur_ts - *ts); + + if (delta > MAX_ENTRIES - 1) + delta = MAX_ENTRIES - 1; + + key = cpu * MAX_ENTRIES + delta; + val = bpf_map_lookup_elem(&my_lat, &key); + if (val) + __sync_fetch_and_add((long *)val, 1); + + return 0; + +} + +char _license[] SEC("license") = "GPL"; +u32 _version SEC("version") = LINUX_VERSION_CODE; diff --git a/samples/bpf/lathist_user.c b/samples/bpf/lathist_user.c new file mode 100644 index 0000000..65da8c1 --- /dev/null +++ b/samples/bpf/lathist_user.c @@ -0,0 +1,103 @@ +/* Copyright (c) 2013-2015 PLUMgrid, http://plumgrid.com + * Copyright (c) 2015 BMW Car IT GmbH + * + * This program is free software; you can redistribute it and/or + * modify it under the terms of version 2 of the GNU General Public + * License as published by the Free Software Foundation. + */ +#include <stdio.h> +#include <unistd.h> +#include <stdlib.h> +#include <signal.h> +#include <linux/bpf.h> +#include "libbpf.h" +#include "bpf_load.h" + +#define MAX_ENTRIES 20 +#define MAX_CPU 4 +#define MAX_STARS 40 + +struct cpu_hist { + long data[MAX_ENTRIES]; + long max; +}; + +static struct cpu_hist cpu_hist[MAX_CPU]; + +static void stars(char *str, long val, long max, int width) +{ + int i; + + for (i = 0; i < (width * val / max) - 1 && i < width - 1; i++) + str[i] = '*'; + if (val > max) + str[i - 1] = '+'; + str[i] = '\0'; +} + +static void print_hist(void) +{ + char starstr[MAX_STARS]; + struct cpu_hist *hist; + int i, j; + + /* clear screen */ + printf("\033[2J"); + + for (j = 0; j < MAX_CPU; j++) { + hist = &cpu_hist[j]; + + /* ignore CPUs without data (maybe offline?) */ + if (hist->max == 0) + continue; + + printf("CPU %d\n", j); + printf(" latency : count distribution\n"); + for (i = 1; i <= MAX_ENTRIES; i++) { + stars(starstr, hist->data[i - 1], hist->max, MAX_STARS); + printf("%8ld -> %-8ld : %-8ld |%-*s|\n", + (1l << i) >> 1, (1l << i) - 1, + hist->data[i - 1], MAX_STARS, starstr); + } + } +} + +static void get_data(int fd) +{ + long key, value; + int c, i; + + for (i = 0; i < MAX_CPU; i++) + cpu_hist[i].max = 0; + + for (c = 0; c < MAX_CPU; c++) { + for (i = 0; i < MAX_ENTRIES; i++) { + key = c * MAX_ENTRIES + i; + bpf_lookup_elem(fd, &key, &value); + + cpu_hist[c].data[i] = value; + if (value > cpu_hist[c].max) + cpu_hist[c].max = value; + } + } +} + +int main(int argc, char **argv) +{ + char filename[256]; + + snprintf(filename, sizeof(filename), "%s_kern.o", argv[0]); + + if (load_bpf_file(filename)) { + printf("%s", bpf_log_buf); + return 1; + } + + while (1) { + get_data(map_fd[1]); + print_hist(); + sleep(5); + } + + return 0; +}
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 <ast@plumgrid.com>. Signed-off-by: Daniel Wagner <daniel.wagner@bmw-carit.de> Cc: Alexei Starovoitov <ast@plumgrid.com> Cc: Alexei Starovoitov <ast@plumgrid.com> Cc: "David S. Miller" <davem@davemloft.net> Cc: Daniel Borkmann <daniel@iogearbox.net> Cc: Ingo Molnar <mingo@kernel.org> 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. This time with code... cheers, daniel changes v2: - forgot to do a git add... 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 ++ samples/bpf/lathist_kern.c | 99 +++++++++++++++++++++++++++++++++++++++++++ samples/bpf/lathist_user.c | 103 +++++++++++++++++++++++++++++++++++++++++++++ 3 files changed, 206 insertions(+) create mode 100644 samples/bpf/lathist_kern.c create mode 100644 samples/bpf/lathist_user.c