Date: Wed, 27 Jun 2012 16:34:55 +0400
From: "Dmitry V. Levin" <ldv@altlinux.org>
To: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
        KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
        Doug Ledford <dledford@redhat.com>, Al Viro <viro@zeniv.linux.org.uk>,
        Serge Hallyn <serge.hallyn@canonical.com>,
        linux-kernel@vger.kernel.org,
        "Kirill A. Shutemov" <kirill@shutemov.name>
Subject: Re: [RFC, PATCH] CLONE_NEWIPC and exit_group()
Message-ID: <20120627123455.GA32171@altlinux.org>
References: <20120626120425.GA10275@otc-wbsnb-06>
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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):

#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) but no
noticeable difference in the real time.


-- 
ldv
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