Commit 5c7fc2d2 authored by Alexei Starovoitov's avatar Alexei Starovoitov Committed by Ingo Molnar
Browse files

samples/bpf: Add IO latency analysis (iosnoop/heatmap) tool 



BPF C program attaches to
blk_mq_start_request()/blk_update_request() kprobe events to
calculate IO latency.

For every completed block IO event it computes the time delta
in nsec and records in a histogram map:

	map[log10(delta)*10]++

User space reads this histogram map every 2 seconds and prints
it as a 'heatmap' using gray shades of text terminal. Black
spaces have many events and white spaces have very few events.
Left most space is the smallest latency, right most space is
the largest latency in the range.

Usage:

	$ sudo ./tracex3
	and do 'sudo dd if=/dev/sda of=/dev/null' in other terminal.

Observe IO latencies and how different activity (like 'make
kernel') affects it.

Similar experiments can be done for network transmit latencies,
syscalls, etc.

'-t' flag prints the heatmap using normal ascii characters:

$ sudo ./tracex3 -t
  heatmap of IO latency
  # - many events with this latency
    - few events
	|1us      |10us     |100us    |1ms      |10ms     |100ms    |1s |10s
				 *ooo. *O.#.                                    # 221
			      .  *#     .                                       # 125
				 ..   .o#*..                                    # 55
			    .  . .  .  .#O                                      # 37
				 .#                                             # 175
				       .#*.                                     # 37
				  #                                             # 199
		      .              . *#*.                                     # 55
				       *#..*                                    # 42
				  #                                             # 266
			      ...***Oo#*OO**o#* .                               # 629
				  #                                             # 271
				      . .#o* o.*o*                              # 221
				. . o* *#O..                                    # 50

Signed-off-by: default avatarAlexei Starovoitov <ast@plumgrid.com>
Cc: Arnaldo Carvalho de Melo <acme@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: David S. Miller <davem@davemloft.net>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/1427312966-8434-9-git-send-email-ast@plumgrid.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent d822a192

samples/bpf/Makefile

+4 −0
Original line number Diff line number Diff line
@@ -8,6 +8,7 @@ hostprogs-y += sockex1 
hostprogs-y += sockex2

hostprogs-y += tracex1

hostprogs-y += tracex2

hostprogs-y += tracex3



test_verifier-objs := test_verifier.o libbpf.o

test_maps-objs := test_maps.o libbpf.o
@@ -16,6 +17,7 @@ sockex1-objs := bpf_load.o libbpf.o sockex1_user.o 
sockex2-objs := bpf_load.o libbpf.o sockex2_user.o

tracex1-objs := bpf_load.o libbpf.o tracex1_user.o

tracex2-objs := bpf_load.o libbpf.o tracex2_user.o

tracex3-objs := bpf_load.o libbpf.o tracex3_user.o



# Tell kbuild to always build the programs

always := $(hostprogs-y)
@@ -23,6 +25,7 @@ always += sockex1_kern.o 
always += sockex2_kern.o

always += tracex1_kern.o

always += tracex2_kern.o

always += tracex3_kern.o



HOSTCFLAGS += -I$(objtree)/usr/include
@@ -31,6 +34,7 @@ HOSTLOADLIBES_sockex1 += -lelf 
HOSTLOADLIBES_sockex2 += -lelf

HOSTLOADLIBES_tracex1 += -lelf

HOSTLOADLIBES_tracex2 += -lelf

HOSTLOADLIBES_tracex3 += -lelf



# point this to your LLVM backend with bpf support

LLC=$(srctree)/tools/bpf/llvm/bld/Debug+Asserts/bin/llc

samples/bpf/tracex3_kern.c

0 → 100644
+89 −0
Original line number Diff line number Diff line 
/* Copyright (c) 2013-2015 PLUMgrid, http://plumgrid.com

 *

 * 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/skbuff.h>

#include <linux/netdevice.h>

#include <linux/version.h>

#include <uapi/linux/bpf.h>

#include "bpf_helpers.h"



struct bpf_map_def SEC("maps") my_map = {

	.type = BPF_MAP_TYPE_HASH,

	.key_size = sizeof(long),

	.value_size = sizeof(u64),

	.max_entries = 4096,

};



/* kprobe is NOT a stable ABI. If kernel internals change this bpf+kprobe

 * example will no longer be meaningful

 */

SEC("kprobe/blk_mq_start_request")

int bpf_prog1(struct pt_regs *ctx)

{

	long rq = ctx->di;

	u64 val = bpf_ktime_get_ns();



	bpf_map_update_elem(&my_map, &rq, &val, BPF_ANY);

	return 0;

}



static unsigned int log2l(unsigned long long n)

{

#define S(k) if (n >= (1ull << k)) { i += k; n >>= k; }

	int i = -(n == 0);

	S(32); S(16); S(8); S(4); S(2); S(1);

	return i;

#undef S

}



#define SLOTS 100



struct bpf_map_def SEC("maps") lat_map = {

	.type = BPF_MAP_TYPE_ARRAY,

	.key_size = sizeof(u32),

	.value_size = sizeof(u64),

	.max_entries = SLOTS,

};



SEC("kprobe/blk_update_request")

int bpf_prog2(struct pt_regs *ctx)

{

	long rq = ctx->di;

	u64 *value, l, base;

	u32 index;



	value = bpf_map_lookup_elem(&my_map, &rq);

	if (!value)

		return 0;



	u64 cur_time = bpf_ktime_get_ns();

	u64 delta = cur_time - *value;



	bpf_map_delete_elem(&my_map, &rq);



	/* the lines below are computing index = log10(delta)*10

	 * using integer arithmetic

	 * index = 29 ~ 1 usec

	 * index = 59 ~ 1 msec

	 * index = 89 ~ 1 sec

	 * index = 99 ~ 10sec or more

	 * log10(x)*10 = log2(x)*10/log2(10) = log2(x)*3

	 */

	l = log2l(delta);

	base = 1ll << l;

	index = (l * 64 + (delta - base) * 64 / base) * 3 / 64;



	if (index >= SLOTS)

		index = SLOTS - 1;



	value = bpf_map_lookup_elem(&lat_map, &index);

	if (value)

		__sync_fetch_and_add((long *)value, 1);



	return 0;

}

char _license[] SEC("license") = "GPL";

u32 _version SEC("version") = LINUX_VERSION_CODE;

samples/bpf/tracex3_user.c

0 → 100644
+150 −0
Original line number Diff line number Diff line 
/* Copyright (c) 2013-2015 PLUMgrid, http://plumgrid.com

 *

 * 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 <stdlib.h>

#include <signal.h>

#include <unistd.h>

#include <stdbool.h>

#include <string.h>

#include <linux/bpf.h>

#include "libbpf.h"

#include "bpf_load.h"



#define ARRAY_SIZE(x) (sizeof(x) / sizeof(*(x)))



#define SLOTS 100



static void clear_stats(int fd)

{

	__u32 key;

	__u64 value = 0;



	for (key = 0; key < SLOTS; key++)

		bpf_update_elem(fd, &key, &value, BPF_ANY);

}



const char *color[] = {

	"\033[48;5;255m",

	"\033[48;5;252m",

	"\033[48;5;250m",

	"\033[48;5;248m",

	"\033[48;5;246m",

	"\033[48;5;244m",

	"\033[48;5;242m",

	"\033[48;5;240m",

	"\033[48;5;238m",

	"\033[48;5;236m",

	"\033[48;5;234m",

	"\033[48;5;232m",

};

const int num_colors = ARRAY_SIZE(color);



const char nocolor[] = "\033[00m";



const char *sym[] = {

	" ",

	" ",

	".",

	".",

	"*",

	"*",

	"o",

	"o",

	"O",

	"O",

	"#",

	"#",

};



bool full_range = false;

bool text_only = false;



static void print_banner(void)

{

	if (full_range)

		printf("|1ns     |10ns     |100ns    |1us      |10us     |100us"

		       "    |1ms      |10ms     |100ms    |1s       |10s\n");

	else

		printf("|1us      |10us     |100us    |1ms      |10ms     "

		       "|100ms    |1s       |10s\n");

}



static void print_hist(int fd)

{

	__u32 key;

	__u64 value;

	__u64 cnt[SLOTS];

	__u64 max_cnt = 0;

	__u64 total_events = 0;



	for (key = 0; key < SLOTS; key++) {

		value = 0;

		bpf_lookup_elem(fd, &key, &value);

		cnt[key] = value;

		total_events += value;

		if (value > max_cnt)

			max_cnt = value;

	}

	clear_stats(fd);

	for (key = full_range ? 0 : 29; key < SLOTS; key++) {

		int c = num_colors * cnt[key] / (max_cnt + 1);



		if (text_only)

			printf("%s", sym[c]);

		else

			printf("%s %s", color[c], nocolor);

	}

	printf(" # %lld\n", total_events);

}



int main(int ac, char **argv)

{

	char filename[256];

	int i;



	snprintf(filename, sizeof(filename), "%s_kern.o", argv[0]);



	if (load_bpf_file(filename)) {

		printf("%s", bpf_log_buf);

		return 1;

	}



	for (i = 1; i < ac; i++) {

		if (strcmp(argv[i], "-a") == 0) {

			full_range = true;

		} else if (strcmp(argv[i], "-t") == 0) {

			text_only = true;

		} else if (strcmp(argv[i], "-h") == 0) {

			printf("Usage:\n"

			       "  -a display wider latency range\n"

			       "  -t text only\n");

			return 1;

		}

	}



	printf("  heatmap of IO latency\n");

	if (text_only)

		printf("  %s", sym[num_colors - 1]);

	else

		printf("  %s %s", color[num_colors - 1], nocolor);

	printf(" - many events with this latency\n");



	if (text_only)

		printf("  %s", sym[0]);

	else

		printf("  %s %s", color[0], nocolor);

	printf(" - few events\n");



	for (i = 0; ; i++) {

		if (i % 20 == 0)

			print_banner();

		print_hist(map_fd[1]);

		sleep(2);

	}



	return 0;

}

CRA Git | Maintained and supported by SUSTech CRA and CCSE