On 24/11/06, David Chinner <dgc@xxxxxxx> wrote:
On Thu, Nov 23, 2006 at 07:37:00PM +0100, Arjan van de Ven wrote: > On Thu, 2006-11-23 at 14:16 +0100, Ingo Oeser wrote: > > Hi there, > > > > David Chinner schrieb: > > > If the softirqs were run on a different stack, then a lot of these > > softirqs DO run on their own stack! So they run on a separate stack for 4k stacks on x86?
Yes, with 4K stacks there's sepperate IRQ stack.
From the help text for CONFIG_4KSTACKS :
"If you say Y here the kernel will use a 4Kb stacksize for the kernel stack attached to each process/thread. This facilitates running more threads on a system and also reduces the pressure on the VM subsystem for higher order allocations. This option will also use IRQ stacks to compensate for the reduced stackspace."
They don't run on a separate stack for 8k stacks on x86 - Jesper's traces show that - so this may indicate an issue with the methodology used to generate the stack overflow traces inteh first place. i.e. if 4k stacks use a separate stack, then most of the reported overflows are spurious and would not normally occur on 4k stack systems..
Well, some of the traces show that we were down to ~3K stack free with 8K stacks, so ~5K used. Even with 4K stacks and sepperate stack for IRQs we will still be uncomfortably close to the edge in those cases. Also, I did manage to capture a single line via netconsole while running with 4K stacks : do_IRQ: stack overflow: 492 Unfortunately that was the only line that made it to the remote log server, so I don't have the actual trace for that one. But it does show that there really is an issue when running with 4K stacks, IRQ stacks or no. -- Jesper Juhl <jesper.juhl@xxxxxxxxx> Don't top-post http://www.catb.org/~esr/jargon/html/T/top-post.html Plain text mails only, please http://www.expita.com/nomime.html - To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
