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

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Message-ID: <20080626060216.1fe210c4@infradead.org>
Date:	Thu, 26 Jun 2008 06:02:16 -0700
From:	Arjan van de Ven <arjan@...radead.org>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	Dave Airlie <airlied@...ux.ie>,
	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 03:36:14 -0700
Arjan van de Ven <arjan@...radead.org> wrote:

> 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
eh never mind this is total bogus
yes a full ipi is needed.

note that with ioremap you may need certain tricks as well to deal with
cache type aliasing, depending on the type of ioremap you want (wc?)

> 
> > 
> > Dave.
> 
> 


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