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readahead.c
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readahead.c
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// SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
// Copyright (c) 2020 Wenbo Zhang
//
// Based on readahead(8) from BPF-Perf-Tools-Book by Brendan Gregg.
// 8-Jun-2020 Wenbo Zhang Created this.
#include <argp.h>
#include <signal.h>
#include <stdio.h>
#include <unistd.h>
#include <bpf/libbpf.h>
#include <bpf/bpf.h>
#include "readahead.h"
#include "readahead.skel.h"
#include "trace_helpers.h"
static struct env {
int duration;
bool verbose;
} env = {
.duration = -1
};
static volatile bool exiting;
const char *argp_program_version = "readahead 0.1";
const char *argp_program_bug_address = "<[email protected]>";
const char argp_program_doc[] =
"Show fs automatic read-ahead usage.\n"
"\n"
"USAGE: readahead [--help] [-d DURATION]\n"
"\n"
"EXAMPLES:\n"
" readahead # summarize on-CPU time as a histogram"
" readahead -d 10 # trace for 10 seconds only\n";
static const struct argp_option opts[] = {
{ "duration", 'd', "DURATION", 0, "Duration to trace"},
{ "verbose", 'v', NULL, 0, "Verbose debug output" },
{},
};
static error_t parse_arg(int key, char *arg, struct argp_state *state)
{
switch (key) {
case 'v':
env.verbose = true;
break;
case 'd':
errno = 0;
env.duration = strtol(arg, NULL, 10);
if (errno || env.duration <= 0) {
fprintf(stderr, "Invalid duration: %s\n", arg);
argp_usage(state);
}
break;
default:
return ARGP_ERR_UNKNOWN;
}
return 0;
}
int libbpf_print_fn(enum libbpf_print_level level,
const char *format, va_list args)
{
if (level == LIBBPF_DEBUG && !env.verbose)
return 0;
return vfprintf(stderr, format, args);
}
static void sig_handler(int sig)
{
exiting = true;
}
static int readahead__set_attach_target(struct bpf_program *prog)
{
int err;
err = bpf_program__set_attach_target(prog, 0, "do_page_cache_ra");
if (!err)
return 0;
err = bpf_program__set_attach_target(prog, 0,
"__do_page_cache_readahead");
if (!err)
return 0;
fprintf(stderr, "failed to set attach target for %s: %s\n",
bpf_program__name(prog), strerror(-err));
return err;
}
int main(int argc, char **argv)
{
static const struct argp argp = {
.options = opts,
.parser = parse_arg,
.doc = argp_program_doc,
};
struct readahead_bpf *obj;
struct hist *histp;
int err;
err = argp_parse(&argp, argc, argv, 0, NULL, NULL);
if (err)
return err;
libbpf_set_print(libbpf_print_fn);
err = bump_memlock_rlimit();
if (err) {
fprintf(stderr, "failed to increase rlimit: %d\n", err);
return 1;
}
obj = readahead_bpf__open();
if (!obj) {
fprintf(stderr, "failed to open BPF object\n");
return 1;
}
/*
* Starting from v5.10-rc1 (8238287), __do_page_cache_readahead has
* renamed to do_page_cache_ra. So we specify the function dynamically.
*/
err = readahead__set_attach_target(obj->progs.do_page_cache_ra);
if (err)
goto cleanup;
err = readahead__set_attach_target(obj->progs.do_page_cache_ra_ret);
if (err)
goto cleanup;
err = readahead_bpf__load(obj);
if (err) {
fprintf(stderr, "failed to load BPF object\n");
goto cleanup;
}
err = readahead_bpf__attach(obj);
if (err) {
fprintf(stderr, "failed to attach BPF programs\n");
goto cleanup;
}
signal(SIGINT, sig_handler);
printf("Tracing fs read-ahead ... Hit Ctrl-C to end.\n");
sleep(env.duration);
printf("\n");
histp = &obj->bss->hist;
printf("Readahead unused/total pages: %d/%d\n",
histp->unused, histp->total);
print_log2_hist(histp->slots, MAX_SLOTS, "msecs");
cleanup:
readahead_bpf__destroy(obj);
return err != 0;
}