Re: [tip:perfcounters/core] x86: Add NMI types for kmap_atomic
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- Subject: Re: [tip:perfcounters/core] x86: Add NMI types for kmap_atomic
- From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
- Date: Wed, 17 Jun 2009 09:58:38 +0200
- Cc: Ingo Molnar <mingo@xxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, mingo@xxxxxxxxxx, hpa@xxxxxxxxx, paulus@xxxxxxxxx, acme@xxxxxxxxxx, efault@xxxxxx, npiggin@xxxxxxx, tglx@xxxxxxxxxxxxx, linux-tip-commits@xxxxxxxxxxxxxxx, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, Tejun Heo <tj@xxxxxxxxxx>
- In-reply-to: <Pine.LNX.4.64.0906161312440.552@xxxxxxxxxxxxx>
- References: <1245080486.6800.561.camel@laptop> <1245089065.13761.19316.camel@twins> <20090615181555.GA11248@xxxxxxx> <1245089943.13761.19334.camel@twins> <20090615182549.GD11248@xxxxxxx> <1245090608.13761.19349.camel@twins> <20090615184217.GG11248@xxxxxxx> <1245091674.6741.180.camel@laptop> <20090615185259.GK11248@xxxxxxx> <1245092433.6741.201.camel@laptop> <20090616081348.GC16229@xxxxxxx> <Pine.LNX.4.64.0906161312440.552@xxxxxxxxxxxxx>
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.
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