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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

  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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