Re: The speed of zsh

[Zoltan Hidvegi <hzoli@cs.elte.hu>]

> } Somehow ksh spawns external commands twice as fast as zsh.
> 
> I suspect it has something to do with zsh's use of pipes for synchronizing
> parent and child processes; the zsh parent doesn't do anything until the
> child finishes its entersubsh() and closes the pipe.  Ksh probably doesn't
> create the pipe in the first place.

It the script I tried there was only a process substitution which does not
use synch pipes.  Anyway I did remove synch calls and it did make zsh a bit
faster even when it executed scripts which never before used synch perhaps
because of the better use of CPU cache.  And I now discovered the real
reason why that particular script was so slow.  Zsh executes process
substitutions after forking.  This means that the commands used in process
substitutions never get hashed in the main process so the path is searched
each time.  After adding hash expr to the script zsh become almost as fast
as ksh.  But builtin-only scripts are still much slower than in ksh :-).

Attached is the patch to remove pipe synchronization code.

Zoltan

*** Src/exec.c	1996/08/25 10:32:58	2.85
--- Src/exec.c	1996/08/25 12:05:46
***************
*** 718,731 ****
  		if ((list_pipe || last1) && !list_pipe_child &&
  		    jn->stat & STAT_STOPPED) {
  		    pid_t pid;
- 		    int synch[2];
- 
- 		    pipe(synch);
  
  		    if ((pid = fork()) == -1) {
  			trashzle();
- 			close(synch[0]);
- 			close(synch[1]);
  			putc('\n', stderr);
  			fprintf(stderr, "zsh: job can't be suspended\n");
  			fflush(stderr);
--- 718,726 ----
***************
*** 734,747 ****
  			thisjob = newjob;
  		    }
  		    else if (pid) {
- 			char dummy;
- 
  			list_pipe_pid = pid;
  			nowait = errflag = 1;
  			breaks = loops;
- 			close(synch[1]);
- 			read(synch[0], &dummy, 1);
- 			close(synch[0]);
  			jobtab[list_pipe_job].other = newjob;
  			jobtab[list_pipe_job].stat |= STAT_SUPERJOB;
  			jn->stat |= STAT_SUBJOB | STAT_NOPRINT;
--- 729,737 ----
***************
*** 750,759 ****
  			break;
  		    }
  		    else {
- 			close(synch[0]);
  			entersubsh(Z_ASYNC, 0, 0);
  			setpgrp(0L, mypgrp = jobtab[list_pipe_job].gleader);
- 			close(synch[1]);
  			kill(getpid(), SIGSTOP);
  			list_pipe = 0;
  			list_pipe_child = 1;
--- 740,747 ----
***************
*** 818,843 ****
  	 * shell command, do foo in a subshell and do the     *
  	 * rest of the pipeline in the current shell.         */
  	if (pline->left->type >= CURSH && (how & Z_SYNC)) {
- 	    int synch[2];
- 
- 	    pipe(synch);
  	    if ((pid = fork()) == -1) {
- 		close(synch[0]);
- 		close(synch[1]);
  		zerr("fork failed: %e", NULL, errno);
  	    } else if (pid) {
! 		char dummy, *text;
  
  		text = getjobtext((void *) pline->left);
  		addproc(pid, text);
- 		close(synch[1]);
- 		read(synch[0], &dummy, 1);
- 		close(synch[0]);
  	    } else {
  		zclose(pipes[0]);
- 		close(synch[0]);
  		entersubsh(how, 2, 0);
- 		close(synch[1]);
  		execcmd(pline->left, input, pipes[1], how, 0);
  		_exit(lastval);
  	    }
--- 806,821 ----
  	 * shell command, do foo in a subshell and do the     *
  	 * rest of the pipeline in the current shell.         */
  	if (pline->left->type >= CURSH && (how & Z_SYNC)) {
  	    if ((pid = fork()) == -1) {
  		zerr("fork failed: %e", NULL, errno);
  	    } else if (pid) {
! 		char *text;
  
  		text = getjobtext((void *) pline->left);
  		addproc(pid, text);
  	    } else {
  		zclose(pipes[0]);
  		entersubsh(how, 2, 0);
  		execcmd(pline->left, input, pipes[1], how, 0);
  		_exit(lastval);
  	    }
***************
*** 1411,1430 ****
          sigtrapped[SIGEXIT] || havefiles()))))) {
  
  	pid_t pid;
- 	int synch[2];
- 	char dummy;
  
  	child_block();
- 	pipe(synch);
  
  	if ((pid = zfork()) == -1) {
- 	    close(synch[0]);
- 	    close(synch[1]);
  	    return;
  	} if (pid) {
- 	    close(synch[1]);
- 	    read(synch[0], &dummy, 1);
- 	    close(synch[0]);
  #ifdef HAVE_DEV_FD
  	    closem(2);
  #endif
--- 1389,1400 ----
***************
*** 1442,1450 ****
  	    return;
  	}
  	/* pid == 0 */
- 	close(synch[0]);
  	entersubsh(how, type != SUBSH && !(how & Z_ASYNC) ? 2 : 1, 0);
- 	close(synch[1]);
  	forked = 1;
  	if (sigtrapped[SIGINT] & ZSIG_IGNORED)
  	    holdintr();
--- 1412,1418 ----