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Date: Wed, 1 Jun 2022 23:31:16 -0700
From: Ian Rogers <irogers@...gle.com>
To: Namhyung Kim <namhyung@...nel.org>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>,
Jiri Olsa <jolsa@...nel.org>, Ingo Molnar <mingo@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
LKML <linux-kernel@...r.kernel.org>,
linux-perf-users@...r.kernel.org, Will Deacon <will@...nel.org>,
Waiman Long <longman@...hat.com>,
Boqun Feng <boqun.feng@...il.com>,
Davidlohr Bueso <dave@...olabs.net>
Subject: Re: [PATCH 5/5] perf lock: Look up callchain for the contended locks
On Tue, May 31, 2022 at 11:58 PM Namhyung Kim <namhyung@...nel.org> wrote:
>
> The lock contention tracepoints don't provide lock names. All we can
> do is to get stack traces and show the caller instead. To minimize
> the overhead it's limited to up to 8 stack traces and display the
> first non-lock function symbol name as a caller.
>
> $ perf lock report -F acquired,contended,avg_wait
>
> Name acquired contended avg wait (ns)
>
> update_blocked_a... 40 40 3611
> kernfs_fop_open+... 5 5 3636
> _nohz_idle_balance 3 3 2650
> tick_do_update_j... 1 1 6041
> ep_scan_ready_list 1 1 3930
> ...
>
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
Acked-by: Ian Rogers <irogers@...gle.com>
Thanks,
Ian
> ---
> tools/perf/builtin-lock.c | 165 +++++++++++++++++++++++++++++++++++++-
> 1 file changed, 161 insertions(+), 4 deletions(-)
>
> diff --git a/tools/perf/builtin-lock.c b/tools/perf/builtin-lock.c
> index 82cbf0f2e4cd..46a5b3b50f0b 100644
> --- a/tools/perf/builtin-lock.c
> +++ b/tools/perf/builtin-lock.c
> @@ -9,6 +9,7 @@
> #include "util/symbol.h"
> #include "util/thread.h"
> #include "util/header.h"
> +#include "util/callchain.h"
>
> #include <subcmd/pager.h>
> #include <subcmd/parse-options.h>
> @@ -19,6 +20,7 @@
> #include "util/tool.h"
> #include "util/data.h"
> #include "util/string2.h"
> +#include "util/map.h"
>
> #include <sys/types.h>
> #include <sys/prctl.h>
> @@ -32,6 +34,7 @@
> #include <linux/kernel.h>
> #include <linux/zalloc.h>
> #include <linux/err.h>
> +#include <linux/stringify.h>
>
> static struct perf_session *session;
>
> @@ -120,6 +123,17 @@ static struct rb_root thread_stats;
> static bool combine_locks;
> static bool show_thread_stats;
>
> +/*
> + * CONTENTION_STACK_DEPTH
> + * Number of stack trace entries to find callers
> + */
> +#define CONTENTION_STACK_DEPTH 8
> +
> +static u64 sched_text_start;
> +static u64 sched_text_end;
> +static u64 lock_text_start;
> +static u64 lock_text_end;
> +
> static struct thread_stat *thread_stat_find(u32 tid)
> {
> struct rb_node *node;
> @@ -451,6 +465,18 @@ static struct lock_stat *pop_from_result(void)
> return container_of(node, struct lock_stat, rb);
> }
>
> +static struct lock_stat *lock_stat_find(u64 addr)
> +{
> + struct hlist_head *entry = lockhashentry(addr);
> + struct lock_stat *ret;
> +
> + hlist_for_each_entry(ret, entry, hash_entry) {
> + if (ret->addr == addr)
> + return ret;
> + }
> + return NULL;
> +}
> +
> static struct lock_stat *lock_stat_findnew(u64 addr, const char *name)
> {
> struct hlist_head *entry = lockhashentry(addr);
> @@ -789,6 +815,116 @@ static int report_lock_release_event(struct evsel *evsel,
> return 0;
> }
>
> +static bool is_lock_function(u64 addr)
> +{
> + if (!sched_text_start) {
> + struct machine *machine = &session->machines.host;
> + struct map *kmap;
> + struct symbol *sym;
> +
> + sym = machine__find_kernel_symbol_by_name(machine,
> + "__sched_text_start",
> + &kmap);
> + if (!sym) {
> + /* to avoid retry */
> + sched_text_start = 1;
> + return false;
> + }
> +
> + sched_text_start = kmap->unmap_ip(kmap, sym->start);
> +
> + /* should not fail from here */
> + sym = machine__find_kernel_symbol_by_name(machine,
> + "__sched_text_end",
> + &kmap);
> + sched_text_end = kmap->unmap_ip(kmap, sym->start);
> +
> + sym = machine__find_kernel_symbol_by_name(machine,
> + "__lock_text_start",
> + &kmap);
> + lock_text_start = kmap->unmap_ip(kmap, sym->start);
> +
> + sym = machine__find_kernel_symbol_by_name(machine,
> + "__lock_text_end",
> + &kmap);
> + lock_text_start = kmap->unmap_ip(kmap, sym->start);
> + }
> +
> + /* failed to get kernel symbols */
> + if (sched_text_start == 1)
> + return false;
> +
> + /* mutex and rwsem functions are in sched text section */
> + if (sched_text_start <= addr && addr < sched_text_end)
> + return true;
> +
> + /* spinlock functions are in lock text section */
> + if (lock_text_start <= addr && addr < lock_text_end)
> + return true;
> +
> + return false;
> +}
> +
> +static int lock_contention_caller(struct evsel *evsel, struct perf_sample *sample,
> + char *buf, int size)
> +{
> + struct thread *thread;
> + struct callchain_cursor *cursor = &callchain_cursor;
> + struct symbol *sym;
> + int skip = 0;
> + int ret;
> +
> + /* lock names will be replaced to task name later */
> + if (show_thread_stats)
> + return -1;
> +
> + thread = machine__findnew_thread(&session->machines.host,
> + -1, sample->pid);
> + if (thread == NULL)
> + return -1;
> +
> + /* use caller function name from the callchain */
> + ret = thread__resolve_callchain(thread, cursor, evsel, sample,
> + NULL, NULL, CONTENTION_STACK_DEPTH);
> + if (ret != 0) {
> + thread__put(thread);
> + return -1;
> + }
> +
> + callchain_cursor_commit(cursor);
> + thread__put(thread);
> +
> + while (true) {
> + struct callchain_cursor_node *node;
> +
> + node = callchain_cursor_current(cursor);
> + if (node == NULL)
> + break;
> +
> + /* skip first 3 entries - for lock functions */
> + if (++skip <= 3)
> + goto next;
> +
> + sym = node->ms.sym;
> + if (sym && !is_lock_function(node->ip)) {
> + struct map *map = node->ms.map;
> + u64 offset;
> +
> + offset = map->map_ip(map, node->ip) - sym->start;
> +
> + if (offset)
> + scnprintf(buf, size, "%s+%#lx", sym->name, offset);
> + else
> + strlcpy(buf, sym->name, size);
> + return 0;
> + }
> +
> +next:
> + callchain_cursor_advance(cursor);
> + }
> + return -1;
> +}
> +
> static int report_lock_contention_begin_event(struct evsel *evsel,
> struct perf_sample *sample)
> {
> @@ -800,9 +936,18 @@ static int report_lock_contention_begin_event(struct evsel *evsel,
> if (show_thread_stats)
> addr = sample->tid;
>
> - ls = lock_stat_findnew(addr, "No name");
> - if (!ls)
> - return -ENOMEM;
> + ls = lock_stat_find(addr);
> + if (!ls) {
> + char buf[128];
> + const char *caller = buf;
> +
> + if (lock_contention_caller(evsel, sample, buf, sizeof(buf)) < 0)
> + caller = "Unknown";
> +
> + ls = lock_stat_findnew(addr, caller);
> + if (!ls)
> + return -ENOMEM;
> + }
>
> ts = thread_stat_findnew(sample->tid);
> if (!ts)
> @@ -1176,6 +1321,7 @@ static int __cmd_report(bool display_info)
> struct perf_tool eops = {
> .sample = process_sample_event,
> .comm = perf_event__process_comm,
> + .mmap = perf_event__process_mmap,
> .namespaces = perf_event__process_namespaces,
> .ordered_events = true,
> };
> @@ -1191,6 +1337,8 @@ static int __cmd_report(bool display_info)
> return PTR_ERR(session);
> }
>
> + /* for lock function check */
> + symbol_conf.sort_by_name = true;
> symbol__init(&session->header.env);
>
> if (!perf_session__has_traces(session, "lock record"))
> @@ -1235,8 +1383,12 @@ static int __cmd_record(int argc, const char **argv)
> const char *record_args[] = {
> "record", "-R", "-m", "1024", "-c", "1", "--synth", "task",
> };
> + const char *callgraph_args[] = {
> + "--call-graph", "fp," __stringify(CONTENTION_STACK_DEPTH),
> + };
> unsigned int rec_argc, i, j, ret;
> unsigned int nr_tracepoints;
> + unsigned int nr_callgraph_args = 0;
> const char **rec_argv;
> bool has_lock_stat = true;
>
> @@ -1261,8 +1413,10 @@ static int __cmd_record(int argc, const char **argv)
> }
> }
>
> + nr_callgraph_args = ARRAY_SIZE(callgraph_args);
> +
> setup_args:
> - rec_argc = ARRAY_SIZE(record_args) + argc - 1;
> + rec_argc = ARRAY_SIZE(record_args) + nr_callgraph_args + argc - 1;
>
> if (has_lock_stat)
> nr_tracepoints = ARRAY_SIZE(lock_tracepoints);
> @@ -1294,6 +1448,9 @@ static int __cmd_record(int argc, const char **argv)
> rec_argv[i++] = ev_name;
> }
>
> + for (j = 0; j < nr_callgraph_args; j++, i++)
> + rec_argv[i] = callgraph_args[j];
> +
> for (j = 1; j < (unsigned int)argc; j++, i++)
> rec_argv[i] = argv[j];
>
> --
> 2.36.1.255.ge46751e96f-goog
>
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