Re: [PATCH 1/3] Separate IRQ-stacks from 4K-stacks option

[Lee Revell]

On Wed, 2004-10-20 at 13:08, Andrea Arcangeli wrote:
> On Wed, Oct 20, 2004 at 12:55:17PM -0400, Lee Revell wrote:
> > This was not my point, I agree that the two have nothing to do with each
> > other.  But if a hardirq handler runs for 3ms then no user code can run
> > for 3ms.  Therefore this is a problem if our goal for desktop response
> > is 1ms.
> 
> I sure agree it's a problem, but not always userspace code needs to run
> for the user not to notice. With ring buffers in the kernel for playback
> all you need is a nested irq for the user not to notice skips.
> 

I was thinking of X, not audio.  This might be a problem for AV
playback.  Maybe that would depend on if DRI was in use.  Anyway I use a
low latency kernel because i need sub-ms response, I was just pointing
out that the current behavior might not be compatible with the 1ms
target.

However with the patch in -mm that enables setting max_sectors_kb, the
1ms goal can be achived by lowering this to 256 or so.  If I were
shipping a desktop distro I would lower this by default.  My tests show
the slowdown is barely measurable if at all.

Lee

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