Re: [tip:perfcounters/core] x86: Add NMI types for kmap_atomic

From: Peter Zijlstra
Date: Wed Jun 17 2009 - 03:59:25 EST

On Tue, 2009-06-16 at 13:38 +0100, Hugh Dickins wrote:
> Something else to throw in: what if they were not just atomic,
> but also replaced the current sleeping kmaps? i.e. a task context
> carries around its own stack of these.

I actually did that once, but it means the task needs to be cpu-affine,
because fixmaps have different addresses between cpus. And disabling
migration for tasks has subtle side-effects so I dropped that again.

However, I recently considered the possiblity of putting the fixmaps in
the new per-cpu address space so that we might use the %gs segment to
normalize the fixmap addresses between the cpus.

This would allow full preemptible kmaps (yay for -rt).

However I suspect it might greatly complicate kmaps for the !i386 world.
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at