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tracing/user_events: Use bits vs bytes for enabled status page data

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User processes may require many events and when they do the cache
performance of a byte index status check is less ideal than a bit index.
The previous event limit per-page was 4096, the new limit is 32,768.

This change adds a bitwise index to the user_reg struct. Programs check
that the bit at status_bit has a bit set within the status page(s).

Link: https://lkml.kernel.org/r/20220728233309.1896-6-beaub@linux.microsoft.com
Link: https://lore.kernel.org/all/2059213643.196683.1648499088753.JavaMail.zimbra@efficios.com/

Suggested-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
This commit is contained in:
Beau Belgrave
2022-07-28 16:33:08 -07:00
committed by Steven Rostedt (Google)
parent d401b72458
commit 39d6d08b2e
5 changed files with 135 additions and 38 deletions
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25
samples/user_events/example.c
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@@ -12,13 +12,21 @@
#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
#include <asm/bitsperlong.h>
#include <endian.h>
#include <linux/user_events.h>
#if __BITS_PER_LONG == 64
#define endian_swap(x) htole64(x)
#else
#define endian_swap(x) htole32(x)
#endif
/* Assumes debugfs is mounted */
const char *data_file = "/sys/kernel/debug/tracing/user_events_data";
const char *status_file = "/sys/kernel/debug/tracing/user_events_status";
static int event_status(char **status)
static int event_status(long **status)
{
int fd = open(status_file, O_RDONLY);
@@ -33,7 +41,8 @@ static int event_status(char **status)
return 0;
}
static int event_reg(int fd, const char *command, int *status, int *write)
static int event_reg(int fd, const char *command, long *index, long *mask,
int *write)
{
struct user_reg reg = {0};
@@ -43,7 +52,8 @@ static int event_reg(int fd, const char *command, int *status, int *write)
if (ioctl(fd, DIAG_IOCSREG, &reg) == -1)
return -1;
*status = reg.status_index;
*index = reg.status_bit / __BITS_PER_LONG;
*mask = endian_swap(1L << (reg.status_bit % __BITS_PER_LONG));
*write = reg.write_index;
return 0;
@@ -51,8 +61,9 @@ static int event_reg(int fd, const char *command, int *status, int *write)
int main(int argc, char **argv)
{
int data_fd, status, write;
char *status_page;
int data_fd, write;
long index, mask;
long *status_page;
struct iovec io[2];
__u32 count = 0;
@@ -61,7 +72,7 @@ int main(int argc, char **argv)
data_fd = open(data_file, O_RDWR);
if (event_reg(data_fd, "test u32 count", &status, &write) == -1)
if (event_reg(data_fd, "test u32 count", &index, &mask, &write) == -1)
return errno;
/* Setup iovec */
@@ -75,7 +86,7 @@ ask:
getchar();
/* Check if anyone is listening */
if (status_page[status]) {
if (status_page[index] & mask) {
/* Yep, trace out our data */
writev(data_fd, (const struct iovec *)io, 2);