From: Roland Dreier <roland@topspin.com>
To: root@chaos.analogic.com
Cc: "Jonathan Lundell" <linux@lundell-bros.com>,
"Jörn Engel" <joern@wohnheim.fh-wedel.de>,
"Linux kernel" <linux-kernel@vger.kernel.org>
Subject: Re: top stack (l)users for 2.5.69
Date: 07 May 2003 11:46:56 -0700 [thread overview]
Message-ID: <52bryeppb3.fsf@topspin.com> (raw)
In-Reply-To: <Pine.LNX.4.53.0305071424290.13499@chaos>
>>>>> "Richard" == Richard B Johnson <root@chaos.analogic.com> writes:
Richard> On Wed, 7 May 2003, Roland Dreier wrote: The kernel
Richard> stack, at least for ix86, is only one, set upon startup
Richard> at 8192 bytes above a label called init_task_unit. The
Richard> kernel must have a separate stack and, contrary to what
Richard> I've been reading on this list, it can't have more kernel
Richard> stacks than CPUs and, I don't see a separate stack
Richard> allocated for different CPUs.
Roland> This is total nonsense. Please don't confuse matters by
Roland> spreading misinformation like this. Every task has a
Roland> separate (8K) kernel stack. Look at the implementation of
Roland> do_fork() and in particular alloc_task_struct().
Roland> If there were only one kernel stack, what do you think
Roland> would happen if a process went to sleep in kernel code?
Richard> No, No. That is a process stack. Every process has it's
Richard> own, entirely seperate stack. This stack is used only in
Richard> user mode. The kernel has it's own stack. Every time you
Richard> switch to kernel mode either by calling the kernel or by
Richard> a hardware interrupt, the kernel's stack is used.
Again, this is nonsense and misinformation. Look at do_fork() and
alloc_task_struct(). Do you see how alloc_task_struct() is just
defined to be __get_free_pages(GFP_KERNEL,1) for i386? Do you
understand that that just allocates two pages (8K) of kernel memory?
Do you see that it is never mapped into userspace, and that anyway
a userspace process can use far more than 8K of stack?
That 8K of memory is used for the kernel stack for a particular
process. When a process makes a system call, that specific stack is
used as the kernel stack.
Richard> When a task sleeps, it sleeps in kernel mode. The kernel
Richard> schedules other tasks until the sleeper has been
Richard> satisfied either by time or by event.
Right. Now think about where the kernel stack for the process that is
sleeping in the kernel is kept.
- Roland
next prev parent reply other threads:[~2003-05-07 18:34 UTC|newest]
Thread overview: 68+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-05-07 13:20 top stack (l)users for 2.5.69 Jörn Engel
2003-05-07 13:45 ` Richard B. Johnson
2003-05-07 13:56 ` Jörn Engel
2003-05-07 14:16 ` Richard B. Johnson
2003-05-07 17:13 ` Jonathan Lundell
2003-05-07 17:40 ` Richard B. Johnson
2003-05-07 18:12 ` Roland Dreier
2003-05-07 18:28 ` Richard B. Johnson
2003-05-07 18:44 ` Timothy Miller
2003-05-07 18:46 ` Roland Dreier [this message]
2003-05-07 19:30 ` Richard B. Johnson
2003-05-07 19:42 ` Roland Dreier
2003-05-07 20:04 ` Richard B. Johnson
2003-05-07 20:23 ` Roland Dreier
2003-05-07 20:42 ` Timothy Miller
2003-05-08 9:06 ` Jörn Engel
2003-05-08 11:33 ` Richard B. Johnson
2003-05-08 12:00 ` Helge Hafting
2003-05-08 15:42 ` Timothy Miller
2003-05-09 8:57 ` Miles Bader
2003-05-09 16:50 ` Timothy Miller
2003-05-08 16:47 ` Davide Libenzi
2003-05-07 18:51 ` Davide Libenzi
2003-05-07 19:22 ` Richard B. Johnson
2003-05-07 19:31 ` Davide Libenzi
2003-05-07 19:39 ` Hua Zhong
2003-05-07 21:47 ` Martin J. Bligh
2003-05-08 10:29 ` David Howells
2003-05-07 17:55 ` Jörn Engel
2003-05-07 16:20 ` Martin J. Bligh
2003-05-07 19:01 ` Dave Hansen
2003-05-07 20:06 ` Jörn Engel
2003-05-07 20:14 ` Dave Hansen
2003-05-08 8:41 ` Jörn Engel
2003-05-08 16:51 ` Dave Hansen
2003-05-08 22:12 ` Jörn Engel
2003-05-07 21:30 ` Jesse Pollard
2003-05-07 21:54 ` Timothy Miller
2003-05-07 22:01 ` Jesse Pollard
2003-05-07 14:33 ` Torsten Landschoff
2003-05-07 14:47 ` William Lee Irwin III
2003-05-07 15:04 ` Torsten Landschoff
2003-05-07 16:01 ` William Lee Irwin III
2003-05-08 15:36 ` Ingo Oeser
2003-05-08 18:04 ` William Lee Irwin III
2003-05-07 15:23 ` Timothy Miller
2003-05-07 15:47 ` William Lee Irwin III
2003-05-07 16:49 ` Jörn Engel
2003-05-07 17:18 ` Davide Libenzi
2003-05-07 17:40 ` Jörn Engel
2003-05-07 18:35 ` Davide Libenzi
2003-05-07 19:45 ` Jörn Engel
2003-05-07 18:23 ` William Lee Irwin III
2003-05-07 17:38 ` William Lee Irwin III
2003-05-07 17:47 ` Jörn Engel
2003-05-07 14:49 ` Richard B. Johnson
2003-05-07 18:36 ` Linus Torvalds
2003-05-07 19:17 ` Jeff Garzik
2003-05-07 20:38 ` Randy.Dunlap
2003-05-07 21:27 ` Marcus Alanen
2003-05-07 21:27 ` Randy.Dunlap
2003-05-08 15:10 ` Ingo Oeser
2003-05-08 17:12 ` Randy.Dunlap
2003-05-07 19:38 Chuck Ebbert
2003-05-08 14:08 Chuck Ebbert
2003-05-08 18:04 ` Jonathan Lundell
2003-05-08 19:05 ` Timothy Miller
2003-05-08 21:00 ` Jonathan Lundell
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