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Date: Tue, 10 Jul 2012 11:50:34 +0300
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
Doug Ledford <dledford@...hat.com>,
Al Viro <viro@...iv.linux.org.uk>,
Serge Hallyn <serge.hallyn@...onical.com>,
linux-kernel@...r.kernel.org, "Dmitry V. Levin" <ldv@...linux.org>,
"Kirill A. Shutemov" <kirill@...temov.name>
Subject: Re: [RFC, PATCH] CLONE_NEWIPC and exit_group()
On Tue, Jun 26, 2012 at 03:04:25PM +0300, Kirill A. Shutemov wrote:
> Hi,
>
> Patch to move kern_unmount() out of exit_group() code path is below.
Andrew, do you have any opinion about the patch?
> Dmitry, could you check if it's beneficial for your use-case?
>
> Results are not that impressive. Microbenchmark:
>
> #define _GNU_SOURCE
> #include <unistd.h>
> #include <sched.h>
> #include <stdlib.h>
> #include <sys/types.h>
> #include <sys/wait.h>
>
> int main(int argc, char *argv[])
> {
> int i;
>
> for (i = 0; i < 1000; i++) {
> if (fork())
> continue;
>
> unshare(CLONE_NEWIPC);
> exit(0);
> }
>
> while (wait(NULL) > 0)
> ;
>
> return 0;
> }
>
> Before:
>
> Performance counter stats for './test' (10 runs):
>
> 2645.849247 task-clock # 3.203 CPUs utilized ( +- 3.43% )
> 2,375 context-switches # 0.001 M/sec ( +- 0.35% )
> 1,579 CPU-migrations # 0.001 M/sec ( +- 0.90% )
> 37,516 page-faults # 0.014 M/sec ( +- 0.44% )
> 5,739,887,800 cycles # 2.169 GHz ( +- 3.50% ) [84.21%]
> 5,126,092,712 stalled-cycles-frontend # 89.31% frontend cycles idle ( +- 3.78% ) [84.47%]
> 3,779,607,146 stalled-cycles-backend # 65.85% backend cycles idle ( +- 4.06% ) [68.26%]
> 1,210,768,660 instructions # 0.21 insns per cycle
> # 4.23 stalled cycles per insn ( +- 1.01% ) [86.28%]
> 213,318,802 branches # 80.624 M/sec ( +- 1.16% ) [84.49%]
> 2,417,038 branch-misses # 1.13% of all branches ( +- 0.70% ) [84.55%]
>
> 0.826165497 seconds time elapsed ( +- 1.26% )
>
> After:
>
> Performance counter stats for './test' (10 runs):
>
> 4248.846649 task-clock # 6.370 CPUs utilized ( +- 13.50% )
> 2,343 context-switches # 0.001 M/sec ( +- 1.51% )
> 1,624 CPU-migrations # 0.000 M/sec ( +- 2.53% )
> 37,416 page-faults # 0.009 M/sec ( +- 0.41% )
> 9,314,096,247 cycles # 2.192 GHz ( +- 13.64% ) [83.75%]
> 8,482,679,429 stalled-cycles-frontend # 91.07% frontend cycles idle ( +- 14.46% ) [83.79%]
> 5,807,497,239 stalled-cycles-backend # 62.35% backend cycles idle ( +- 14.79% ) [67.65%]
> 1,556,594,531 instructions # 0.17 insns per cycle
> # 5.45 stalled cycles per insn ( +- 5.41% ) [85.00%]
> 282,682,358 branches # 66.532 M/sec ( +- 5.56% ) [84.32%]
> 2,610,583 branch-misses # 0.92% of all branches ( +- 4.42% ) [83.90%]
>
> 0.667023551 seconds time elapsed ( +- 12.10% )
>
> Any thoughts if it makes sense?
>
> diff --git a/include/linux/ipc_namespace.h b/include/linux/ipc_namespace.h
> index 5499c92..1a4cfd8 100644
> --- a/include/linux/ipc_namespace.h
> +++ b/include/linux/ipc_namespace.h
> @@ -67,6 +67,8 @@ struct ipc_namespace {
>
> /* user_ns which owns the ipc ns */
> struct user_namespace *user_ns;
> +
> + struct work_struct free_ns_work;
> };
>
> extern struct ipc_namespace init_ipc_ns;
> diff --git a/ipc/namespace.c b/ipc/namespace.c
> index f362298c..edbf885 100644
> --- a/ipc/namespace.c
> +++ b/ipc/namespace.c
> @@ -16,6 +16,8 @@
>
> #include "util.h"
>
> +static void free_ns(struct work_struct *work);
> +
> static struct ipc_namespace *create_ipc_ns(struct task_struct *tsk,
> struct ipc_namespace *old_ns)
> {
> @@ -27,6 +29,7 @@ static struct ipc_namespace *create_ipc_ns(struct task_struct *tsk,
> return ERR_PTR(-ENOMEM);
>
> atomic_set(&ns->count, 1);
> + INIT_WORK(&ns->free_ns_work, free_ns);
> err = mq_init_ns(ns);
> if (err) {
> kfree(ns);
> @@ -116,6 +119,15 @@ static void free_ipc_ns(struct ipc_namespace *ns)
> kfree(ns);
> }
>
> +static void free_ns(struct work_struct *work)
> +{
> + struct ipc_namespace *ns = container_of(work, struct ipc_namespace,
> + free_ns_work);
> +
> + mq_put_mnt(ns);
> + free_ipc_ns(ns);
> +}
> +
> /*
> * put_ipc_ns - drop a reference to an ipc namespace.
> * @ns: the namespace to put
> @@ -137,8 +149,7 @@ void put_ipc_ns(struct ipc_namespace *ns)
> if (atomic_dec_and_lock(&ns->count, &mq_lock)) {
> mq_clear_sbinfo(ns);
> spin_unlock(&mq_lock);
> - mq_put_mnt(ns);
> - free_ipc_ns(ns);
> + schedule_work(&ns->free_ns_work);
> }
> }
>
> --
> Kirill A. Shutemov
--
Kirill A. Shutemov
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