Re: [PATCH] i386: Fix softirq accounting with 4K stacks

[Arjan van de Ven <arjan@infradead.org>]

On Sun, 2006-06-25 at 16:24 +0200, Björn Steinbrink wrote:
> Copy the softirq bits in preempt_count from the current context into the
> hardirq context when using 4K stacks to make the softirq_count macro work
> correctly and thereby fix softirq cpu time accounting.
> 
> Signed-off-by: Björn Steinbrink <B.Steinbrink@gmx.de>
> 
> diff -Nurp a/arch/i386/kernel/irq.c b/arch/i386/kernel/irq.c
> --- a/arch/i386/kernel/irq.c	2006-03-20 06:53:29.000000000 +0100
> +++ b/arch/i386/kernel/irq.c	2006-06-25 15:49:52.000000000 +0200
> @@ -95,6 +95,14 @@ fastcall unsigned int do_IRQ(struct pt_r
>  		irqctx->tinfo.task = curctx->tinfo.task;
>  		irqctx->tinfo.previous_esp = current_stack_pointer;
>  
> +		/*
> +		 * Copy the softirq bits in preempt_count so that the
> +		 * softirq checks work in the hardirq context.
> +		 */
> +		irqctx->tinfo.preempt_count =
> +			irqctx->tinfo.preempt_count & ~SOFTIRQ_MASK |
> +			curctx->tinfo.preempt_count & SOFTIRQ_MASK;
> +
>  		asm volatile(
>  			"       xchgl   %%ebx,%%esp      \n"
>  			"       call    __do_IRQ         \n"

Hi,

at first I got nervous about the asymmetry of this (eg why only do this
copying only on entry, and not a copy back on exit)... but then again
these bits shouldn't change so your patch is ok as is...
it's regrettable that we need to add this for the softirq accounting;
part of me wishes we would just count irq-vs-user time and be done with
it ;)


Acked-by: Arjan van de Ven <arjan@linux.intel.com>