Re: [RFC, PATCH] CLONE_NEWIPC and exit_group()

[Serge Hallyn <serge.hallyn@canonical.com>]

Quoting Dmitry V. Levin (ldv@altlinux.org):
> Hi,
> 
> On Tue, Jun 26, 2012 at 03:04:26PM +0300, Kirill A. Shutemov wrote:
> > Patch to move kern_unmount() out of exit_group() code path is below.
> > Dmitry, could you check if it's beneficial for your use-case?
> 
> I've benchmarked a slightly modified test which is closer to our use-case
> (child processes are forked sequentially):

Did you run this in parallel, perhaps with numcpus/2 jobs plus a
hackbench running on the side?

> #define _GNU_SOURCE
> #include <unistd.h>
> #include <sched.h>
> #include <stdlib.h>
> #include <sys/wait.h>
> 
> int
> main(void)
> {
> 	int i;
> 	for (i = 0; i < 1024; i++) {
> 		if (fork()) {
> 			wait(NULL);
> 			continue;
> 		}
> 		unshare(CLONE_NEWIPC);
> 		exit(0);
> 	}
> 	return 0;
> }
> 
> On 3.4.4 with rcu_barrier patch:
> 0.09user 0.00system 0:32.77elapsed 0%CPU (0avgtext+0avgdata 1472maxresident)k
> 0inputs+0outputs (0major+38017minor)pagefaults 0swaps
> 
> On 3.4.4 with rcu_barrier patch and your new patch:
> 0.00user 0.06system 0:32.77elapsed 0%CPU (0avgtext+0avgdata 1472maxresident)k
> 0inputs+0outputs (0major+38017minor)pagefaults 0swaps
> 
> So there is a clear difference in accounting (user vs system)

Yup, I'd argue that's a bad thing :)

> but no
> noticeable difference in the real time.

Thanks for testing!

-serge