From: Takeharu KATO <kato.takeharu@jp•fujitsu.com>
To: Benjamin Herrenschmidt <benh@kernel•crashing.org>
Cc: linuxppc-dev list <linuxppc-dev@ozlabs•org>
Subject: Re: boot time scheduling hile atomic
Date: Wed, 16 Mar 2005 14:24:41 +0900 [thread overview]
Message-ID: <4237C319.4050109@jp.fujitsu.com> (raw)
In-Reply-To: <1110932285.25201.66.camel@gaston>
Hi Benjamin:
Thank you for your response.
> I think the problem is more why are we calling a syscall while the
> preempt count is up ?
>
Because, start_kernel(line:455) in init/main.c count up this.
-- start_kernel (init/main.c)
451 /*
452 * Disable preemption - early bootup scheduling is extremely
453 * fragile until we cpu_idle() for the first time.
454 */
455 preempt_disable();
456 build_all_zonelists();
-- start_kernel(init/main.c)
Preemption is disabled until it enters the body of idle task from rest_init.
Please see below:
-- rest_init (init/main.c)
379 static void noinline rest_init(void)
380 __releases(kernel_lock)
381 {
382 kernel_thread(init, NULL, CLONE_FS | CLONE_SIGHAND);
383 numa_default_policy();
384 unlock_kernel();
385 preempt_enable_no_resched();
386 cpu_idle();
387 }
--
I think that the kernel assumes that init thread(the kernel thread which become to
init process later) is kicked by idle process(cpu_idle).
But, the kernel invoke a system call trap when it execute kernel_thread call
(at rest_init line:382) on PowerPC.
The preemption count has positive value here.
So, PowerPC linux kernel invoke system call when the preempt count is up.
Regards,
--
Takeharu KATO
Fujitsu Limited
Email:kato.takeharu at jp.fujitsu.com
next prev parent reply other threads:[~2005-03-16 5:25 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-03-03 12:44 GCC4 fun Joerg Dorchain
2005-03-03 13:13 ` Marc Leeman
2005-03-03 13:46 ` evilninja
2005-03-03 14:18 ` boot time scheduling hile atomic (was: GCC4 fun.) Joerg Dorchain
2005-03-04 7:57 ` Joerg Dorchain
2005-03-04 15:06 ` boot time scheduling hile atomic _evil
2005-03-10 4:51 ` Takeharu KATO
2005-03-10 7:28 ` Joerg Dorchain
2005-03-10 16:19 ` Takeharu KATO
2005-03-11 6:19 ` Takeharu KATO
2005-03-16 0:18 ` Benjamin Herrenschmidt
2005-03-16 5:24 ` Takeharu KATO [this message]
2005-03-16 5:49 ` Takeharu KATO
2005-03-16 6:28 ` Benjamin Herrenschmidt
2005-03-16 14:07 ` Takeharu KATO
2005-03-16 22:28 ` Benjamin Herrenschmidt
2005-03-17 0:46 ` Takeharu KATO
2005-03-11 22:21 ` boot time scheduling while atomic Takeharu KATO
-- strict thread matches above, loose matches on Subject: below --
2005-06-10 14:23 boot time scheduling hile atomic Rune Torgersen
2005-06-14 12:41 ` Takeharu KATO
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