[PATCH 2/2] lib kallsyms: parse using io api

Ian Rogers
2020-04-30T19:36:08Z

Perf record will call kallsyms__parse 4 times during startup and process
megabytes of data. This changes kallsyms__parse to use the io library
rather than fgets to improve performance of the user code by over 8%.

Before:
Running 'internals/kallsyms-parse' benchmark:
Average kallsyms__parse took: 103.988 ms (+- 0.203 ms)
After:
Running 'internals/kallsyms-parse' benchmark:
Average kallsyms__parse took: 95.571 ms (+- 0.006 ms)

For a workload like:
$ perf record /bin/true
Run under 'perf record -e cycles:u -g' the time goes from:
Before
30.10% 1.67% perf perf [.] kallsyms__parse
After
25.55% 20.04% perf perf [.] kallsyms__parse
So a little under 5% of the start-up time is removed. A lot of what
remains is on the kernel side, but caching kallsyms within perf would
at least impact memory footprint.

Signed-off-by: Ian Rogers <irogers@google.com>
---
tools/lib/api/io.h | 3 ++
tools/lib/symbol/kallsyms.c | 81 +++++++++++++++++++------------------
2 files changed, 44 insertions(+), 40 deletions(-)

diff --git a/tools/lib/api/io.h b/tools/lib/api/io.h
index b7e55b5f8a4a..777c20f6b604 100644
--- a/tools/lib/api/io.h
+++ b/tools/lib/api/io.h
@@ -7,6 +7,9 @@
#ifndef __API_IO__
#define __API_IO__

+#include <stdlib.h>
+#include <unistd.h>
+
struct io {
/* File descriptor being read/ */
int fd;
diff --git a/tools/lib/symbol/kallsyms.c b/tools/lib/symbol/kallsyms.c
index 1a7a9f877095..1ef61b68332a 100644
--- a/tools/lib/symbol/kallsyms.c
+++ b/tools/lib/symbol/kallsyms.c
@@ -1,7 +1,9 @@
// SPDX-License-Identifier: GPL-2.0
#include "symbol/kallsyms.h"
+#include "api/io.h"
#include <stdio.h>
-#include <stdlib.h>
+#include <sys/stat.h>
+#include <fcntl.h>

u8 kallsyms2elf_type(char type)
{
@@ -28,61 +30,60 @@ int hex2u64(const char *ptr, u64 *long_val)
return p - ptr;
}

+static void read_to_eol(struct io *io)
+{
+ int ch;
+
+ for (;;) {
+ ch = io__get_char(io);
+ if (ch < 0 || ch == '\n')
+ return;
+ }
+}
+
int kallsyms__parse(const char *filename, void *arg,
int (*process_symbol)(void *arg, const char *name,
char type, u64 start))
{
- char *line = NULL;
- size_t n;
- int err = -1;
- FILE *file = fopen(filename, "r");
+ struct io io;
+ char bf[BUFSIZ];

- if (file == NULL)
- goto out_failure;
+ io.fd = open(filename, O_RDONLY, 0);

- err = 0;
-
- while (!feof(file)) {
- u64 start;
- int line_len, len;
- char symbol_type;
- char *symbol_name;
-
- line_len = getline(&line, &n, file);
- if (line_len < 0 || !line)
- break;
+ if (io.fd < 0)
+ return -1;

- line[--line_len] = '\0'; /* \n */
+ io__init(&io, io.fd, bf, sizeof(bf));

- len = hex2u64(line, &start);
+ while (!io.eof) {
+ __u64 start;
+ int ch, err;
+ size_t i;
+ char symbol_type;
+ char symbol_name[KSYM_NAME_LEN + 1];

- /* Skip the line if we failed to parse the address. */
- if (!len)
+ if (io__get_hex(&io, &start) != ' ') {
+ read_to_eol(&io);
continue;
-
- len++;
- if (len + 2 >= line_len)
+ }
+ symbol_type = io__get_char(&io);
+ if (io__get_char(&io) != ' ') {
+ read_to_eol(&io);
continue;
-
- symbol_type = line[len];
- len += 2;
- symbol_name = line + len;
- len = line_len - len;
-
- if (len >= KSYM_NAME_LEN) {
- err = -1;
- break;
}
+ for (i = 0; i < sizeof(symbol_name); i++) {
+ ch = io__get_char(&io);
+ if (ch < 0 || ch == '\n')
+ break;
+ symbol_name[i] = ch;
+ }
+ symbol_name[i] = '\0';

err = process_symbol(arg, symbol_name, symbol_type, start);
if (err)
break;
}

- free(line);
- fclose(file);
- return err;
-
-out_failure:
- return -1;
+ close(io.fd);
+ return 0;
}
--
2.26.2.526.g744177e7f7-goog