Re: [LTP] [PATCH V2 2/2] msgctl11: process message queues by portions

[chrubis@suse.cz]

Hi!
> > On my systems /proc/sys/kernel/pid_max is set to 32768 and MSGMNI is
> > from 2000 to 7000 on most of the machines I've seen. So the value of
> > maxnkids was between 1 and 4 previously but it defaults to 10 after this
> > patch which increases the test runtime by minute or two.
> >
> > Thinking of this again the most behavior preserving change would be:
> >
> > 	if ((MSGMNI * MAXNKIDS * 2) > (free_pids / 2))
> > 	        maxnkids = MAX(1, ((free_pids / 4) / MSGMNI));
> >
> > Which would scale the number of kids to the free pids but will not abort
> > the test if there is not enough free pids. The drawback is that the code
> > is complicated enough even without this change...
> >
> 
> According to the definition of recompute_msgmni() function (ipc/msg.c) 
> the limit by which the kernel may increase msgmni automatically is 
> IPCMNI. And IPCMNI is defined to be 32768 (include/linux/ipc.h).
> 
> So yes, the above approach (using MAX) should work on most systems 
> (maybe even all. I'm not sure about embedded stuff) where neither 
> pid_max nor msgmni values were modified manually. Manually changing 
> pid_max and/or msgmni values we can break the test.
> 
> Actually, I don't like the MAX-variant, because of the drawback you 
> mentioned. But the MAX-variant is sufficient for my needs.
> 
> So which patch set to prepare? :)

I would be inclined to set the default maxnkids value to something more
reasonable than 10, perhaps 2 or 3 would be a good compromise between
the test runtime and the amount of system stress the test does.

-- 
Cyril Hrubis
chrubis@suse.cz

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