Re: more on exit performance

David Laight wrote:
> >  (2) for (pid == -1), we can keep the stopped and dead children on
> >      separate lists, and only look at the list(s) that we care about.
> 
> Why not just requeue a stopped child at the top of the sibling list?
> It will save all the extra pointers (and data structures to get wrong!).
> I don't know how how many children the benchmark process has, but I
> suspet it is a lot!  Even then this gains <10%, for a normal process
> (and system workload) it must be noise.

It would be very easy to optimize the WAIT_ANY zombie lookup by looking
at zombproc - that list should be mostly empty and the lookup
should be faster than loop over children.

> >  (3) for (pid < -1), we can similarly look up the pgrp in pid_table
> >      and keep the stopped and dead children on separate lists in the pgrp.
> 
> Can't possibly happen often enough to worry about.

Yeah, I don't think wait on pgrp is used very often.
 
> 	David
> 
> Index: kern_exit.c
> ===================================================================
> RCS file: /cvsroot/src/sys/kern/kern_exit.c,v
> retrieving revision 1.124
> diff -u -p -r1.124 kern_exit.c
> --- kern_exit.c	2003/09/16 13:46:24	1.124
> +++ kern_exit.c	2003/11/02 10:39:49
> @@ -718,10 +727,16 @@ find_stopped_child(struct proc *parent, 
>  	for (;;) {
>  		c_found = 0;
>  		LIST_FOREACH(child, &parent->p_children, p_sibling) {
> -			if (pid != WAIT_ANY &&
> -			    child->p_pid != pid &&
> -			    child->p_pgid != -pid)
> -				continue;
> +			if (pid >= 0) {
> +				if (child->p_pid != pid) {
> +					child = pfind(pid);
> +					if (child == NULL
> +					    || child->p_parent != parent)
> +						break;

This should be outside the LIST_FOREACH() loop. Also, this only
optimizes asleep child lookup, not zombie lookup. Given that
more frequent operation is wait for deceased child, we should
optimize that operation too.
 
> +				}
> +			} else
> +				if (pid != WAIT_ANY && child->p_pgid != -pid)
> +					continue;
>  			/*
>  			 * Wait for processes with p_exitsig != SIGCHLD
>  			 * processes only if WALTSIG is set; wait for
> @@ -730,8 +745,11 @@ find_stopped_child(struct proc *parent, 
>  			 */
>  			if (((options & WALLSIG) == 0) &&
>  			    (options & WALTSIG ? child->p_exitsig == SIGCHLD
> -						: P_EXITSIG(child) != SIGCHLD))
> +						: P_EXITSIG(child) != SIGCHLD)){
> +				if (child->p_pid == pid)
> +					break;
>  				continue;
> +			}
>  
>  			c_found = 1;
>  			if (child->p_stat == SZOMB &&
> @@ -748,6 +766,8 @@ find_stopped_child(struct proc *parent, 
>  				*child_p = child;
>  				return 0;
>  			}
> +			if (child->p_pid == pid)
> +				break;
>  		}
>  		if (c_found == 0)
>  			return ECHILD;
> -- 
> David Laight: [email protected]
> 

-- 
Jaromir Dolecek <[email protected]>            http://www.NetBSD.cz/
-=- We should be mindful of the potential goal, but as the tantric    -=-
-=- Buddhist masters say, ``You may notice during meditation that you -=-
-=- sometimes levitate or glow.   Do not let this distract you.''     -=-