Messages in this thread | | | Date | Mon, 14 Nov 2011 16:46:49 +0400 | From | Ilya Zykov <> | Subject | [PATCH v3 1/2] TTY: tty flip buffer optimisation. |
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Currently, free flip buffer (tty->buf.free) reserve memory for further used, only if driver send to ldisc less 257 bytes in one time. If driver send more, flip buffer reserve(kmalloc()) and then free(kfree()) every chunk more 256 bytes every time.
For testing I use little program that write in loop, argv[1] bytes from one side pty and read on the other. I get follow results:
ilya@serh:~/src/pty$ time ./bench_pty_buf 253 chunk = 253. loop = 3952569. real 0m22.398s user 0m0.604s sys 0m19.545s
ilya@serh:~/src/pty$ time ./bench_pty_buf 255 chunk = 255. loop = 3921568. real 0m20.437s user 0m0.532s sys 0m16.621s
ilya@serh:~/src/pty$ time ./bench_pty_buf 257 chunk = 257. loop = 3891050. real 0m26.367s user 0m0.552s sys 0m28.010s
We can see that on 257 size chunk we loose ~20-30% performance. The time's real was expected ~20-19 sek.
Program bench_pty_buf.c: --- #include <stdio.h> #include <fcntl.h> #include <sys/ioctl.h> #include <termios.h>
#define WRITE_SIZE 1000000000
int main(int argc,char *argv[]) { char pty_name[24]; int mfd, sfd, ptn, chunk, loop; if(argc != 2) goto error_exit; if((chunk = atoi(argv[1])) <= 0) goto error_exit; loop = WRITE_SIZE/chunk; printf("chunk = %d. loop = %d.\n",chunk, loop); mfd = -1; sfd = -1; mfd = open("/dev/ptmx", O_RDWR); if (mfd < 0) { printf("Couldn't open /dev/ptmx %m"); goto error_exit; } if (ioctl(mfd, TIOCGPTN, &ptn) < 0) { printf("Couldn't get pty number %m"); goto error_exit; } snprintf(pty_name, sizeof(pty_name), "/dev/pts/%d", ptn); ptn = 0; if (ioctl(mfd, TIOCSPTLCK, &ptn) < 0) { printf("Couldn't unlock pty slave %s: %m", pty_name); goto error_exit; } if ((sfd = open(pty_name, O_RDWR | O_NOCTTY)) < 0) { printf("Couldn't open pty slave %s: %m", pty_name); goto error_exit; } struct termios tios; cfmakeraw(&tios); if(tcsetattr(sfd, TCSAFLUSH, &tios) < 0) { printf("Can't set raw mode pty slave %s.\n", pty_name); goto error_exit; } char buf[] = { [0 ... 65535] = '1' }; int child; int count; int ret, fillcount; /* Fill buffers without blocked "flip free = 65536" and "N_TTY_BUF_SIZE = 4096" */ for(count = 0; count < 270; count++) { ret = write(sfd,buf,256); if(ret < 0) { printf("Couldn't fill pty master %s count = %d: %m", pty_name, count); goto error_exit; } fillcount += ret; } if ( !(child=fork()) ) { // Child for(count = 0; count < loop*chunk + fillcount; count += ret) { if((ret = read(mfd,buf,chunk)) < 0) { printf("Read: Count = %d, chunk = %d, error = %m \n",count,chunk); goto error_exit; } } goto normal_exit; } // Parent if (child < 0) goto error_exit; for(count = 0; count < loop*chunk; count += ret) { if((ret = write(sfd, buf, chunk)) < 0) { printf("Write: Count = %d, chunk = %d, error = %m \n",count,chunk); goto error_exit; } } int status; waitpid(child,&status,0); if(status) goto error_exit; normal_exit: if (sfd >= 0) close(sfd); if (mfd >= 0) close(mfd); return 0; error_exit: if (sfd >= 0) close(sfd); if (mfd >= 0) close(mfd); return -1; }
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