Hi,
This series introduce new uAPI(RPMSG_CREATE_EPT_FD_IOCTL) for rpmsg
subsystem.
Current uAPI implementation for rpmsg ctrl & char device manipulation is
abstracted in procedures below:
- fd = open("/dev/rpmsg_ctrlX")
- ioctl(fd, RPMSG_CREATE_EPT_IOCTL, &info); /dev/rpmsgY devnode is
generated.
- fd_ep = open("/dev/rpmsgY", O_RDWR)
- operations on fd_ep(write, read, poll ioctl)
- ioctl(fd_ep, RPMSG_DESTROY_EPT_IOCTL)
- close(fd_ep)
- close(fd)
This /dev/rpmsgY abstraction is less favorable for:
- Performance issue: It's time consuming for some operations are
invovled:
- Device node creation.
Depends on specific config, especially CONFIG_DEVTMPFS, the overall
overhead is based on coordination between DEVTMPFS and userspace
tools such as udev and mdev.
- Extra kernel-space switch cost.
- Other major costs brought by heavy-weight logic like device_add().
- /dev/rpmsgY node can be opened only once. It doesn't make much sense
that a dynamically created device node can be opened only once.
- For some container application such as docker, a client can't access
host's dev unless specified explicitly. But in case of /dev/rpmsgY, which
is generated dynamically and whose existence is unknown for clients in
advance, this uAPI based on device node doesn't fit well.
An anon inode based approach is introduced to address the issues above.
Rather than generating device node and opening it, rpmsg code just make
a anon inode representing eptdev and return the fd to userspace.
# Performance demo
An simple C application is tested to verify performance of new uAPI.
$ cat test.c
#include <linux/rpmsg.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/ioctl.h>
#include <fcntl.h>
#include <string.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <errno.h>
#include <sys/time.h>
#define N (1 << 20)
int main(int argc, char *argv[])
{
int ret, fd, ep_fd, loop;
struct rpmsg_endpoint_info info;
struct rpmsg_endpoint_fd_info fd_info;
struct timeval start, end;
int i = 0;
double t1, t2;
fd = -1;
ep_fd = -1;
loop = N;
if (argc == 1) {
loop = N;
} else if (argc > 1) {
loop = atoi(argv[1]);
}
printf("loop[%d]\n", loop);
strcpy(info.name, "epx");
info.src = -1;
info.dst = -1;
strcpy(fd_info.name, "epx");
fd_info.src = -1;
fd_info.dst = -1;
fd_info.fd = -1;
while (fd < 0) {
fd = open("/dev/rpmsg_ctrl0", O_RDWR);
if (fd < 0) {
printf("open rpmsg_ctrl0 failed, fd[%d]\n", fd);
}
}
gettimeofday(&start, NULL);
while (loop--) {
ret = ioctl(fd, RPMSG_CREATE_EPT_IOCTL, &info);
if (ret < 0) {
printf("ioctl[RPMSG_CREATE_EPT_IOCTL] failed,
ret[%d]\n", ret);
}
ep_fd = -1;
i = 0;
while (ep_fd < 0) {
ep_fd = open("/dev/rpmsg0", O_RDWR);
if (ep_fd < 0) {
i++;
printf("open rpmsg0 failed, epfd[%d]\n", ep_fd);
}
}
//printf("Number of open failed[%d]\n", i);
ret = ioctl(ep_fd, RPMSG_DESTROY_EPT_IOCTL, &info);
if (ret < 0) {
printf("old ioctl[RPMSG_DESTROY_EPT_IOCTL] failed,
ret[%d], errno[%d]\n",
ret, errno);
}
close(ep_fd);
}
gettimeofday(&end, NULL);
printf("time for old way: [%ld] us\n", 1000000 * (end.tv_sec -
start.tv_sec) + end.tv_usec - start.tv_usec);
t1 = 1000000 * (end.tv_sec - start.tv_sec) + end.tv_usec -
start.tv_usec;
if (argc == 1) {
loop = N;
} else if (argc > 1) {
loop = atoi(argv[1]);
}
printf("loop[%d]\n", loop);
gettimeofday(&start, NULL);
while (loop--) {
fd_info.fd = -1;
ret = ioctl(fd, RPMSG_CREATE_EPT_FD_IOCTL, &fd_info);
if (ret < 0 || fd_info.fd < 0) {
printf("ioctl[RPMSG_CREATE_EPT_FD_IOCTL] failed,
ret[%d]\n", ret);
}
ret = ioctl(fd_info.fd, RPMSG_DESTROY_EPT_IOCTL, &info);
if (ret < 0) {
printf("new ioctl[RPMSG_DESTROY_EPT_IOCTL] failed,
ret[%d]\n", ret);
}
close(fd_info.fd);
}
gettimeofday(&end, NULL);
printf("time for new way: [%ld] us\n", 1000000 * (end.tv_sec -
start.tv_sec) + end.tv_usec - start.tv_usec);
t2 = 1000000 * (end.tv_sec - start.tv_sec) + end.tv_usec -
start.tv_usec;
printf("t1(old) / t2(new) = %f\n", t1 / t2);
close(fd);
}
# Performance benchmark
- Legacy means benchmark based on old uAPI
- New means benchmark based on new uAPI(the one this series introduce)
- Time are in units of us(10^-6 s)
Test loops Total time(legacy) Total time(new) legacy/new
1 1000 203227 2533 80.2
2 1000 196501 2384 82.4
3 1000 213619 2518 84.8
4 1000 215898 2515 85.8
5 1000 211340 2417 87.4
6 1000 217008 2545 85.2
7 1000 213591 2478 86.1
8 1000 214618 2351 91.2
9 1000 208021 2505 83.0
10 1000 217092 2716 79.9
11 10000 2040802 26765 76.2
12 10000 2027708 26867 75.4
13 10000 1986117 27151 73.1
14 10000 1992956 26301 75.7
15 10000 1980262 25808 76.7
16 10000 1925883 27926 68.9
17 10000 1957518 27100 72.2
18 10000 1980626 28020 70.6
19 10000 1990349 27351 72.7
20 10000 1979087 27563 71.8
21 100000 20266414 256170 79.1
22 100000 19732259 259883 75.9
23 100000 19878399 253710 78.3
24 100000 19788886 257199 76.9
25 100000 19937663 258865 77.0
26 100000 19602512 256771 76.3
27 100000 19599214 257088 76.2
28 100000 19795920 261488 75.7
29 100000 19719341 263299 74.8
30 100000 19871390 258465 76.8
Dawei Li (3):
rpmsg: char: Reuse eptdev logic for anon device
rpmsg: char: Implement eptdev based on anon inode
rpmsg: ctrl: Introduce RPMSG_CREATE_EPT_FD_IOCTL uAPI
drivers/rpmsg/rpmsg_char.c | 124 ++++++++++++++++++++++++++++++-------
drivers/rpmsg/rpmsg_char.h | 19 ++++++
drivers/rpmsg/rpmsg_ctrl.c | 37 ++++++++---
include/uapi/linux/rpmsg.h | 19 ++++++
4 files changed, 167 insertions(+), 32 deletions(-)
---
base-commit: 92a09c47464d040866cf2b4cd052bc60555185fb
Thanks,
Dawei
--
2.25.1
