linux-kernel - Re: kmap_atomic_pfn for PCI BAR access?

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Date:	Thu, 26 Jun 2008 03:36:14 -0700
From:	Arjan van de Ven <arjan@...radead.org>
To:	Dave Airlie <airlied@...ux.ie>
Cc:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Keith Packard <keithp@...thp.com>,
	Dave Airlie <airlied@...il.com>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: kmap_atomic_pfn for PCI BAR access?

On Thu, 26 Jun 2008 07:02:15 +0100 (IST)
Dave Airlie <airlied@...ux.ie> wrote:

> > >   
> > 
> > Anything that does any kind of pagetable manipulation needs to do
> > tlb flushes. kunmap_atomic handles the flushing.
> 
> It doesn't however need to do an IPI dance which is the worst part of 
> doing a tlb flush on SMP machines.
> 
> flushing local CPU tlbs is bad, but doing IPIs and waiting for
> everyone else is brutal.

but you only do IPI's for the multithreaded case to cpus where you're
running; otoh I guess games are multithreaded nowadays

> 
> Dave.


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