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From: David Mosberger <davidm@hpl.hp.com>
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Date: Tue, 4 Dec 2001 09:43:02 -0800
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: tony.luck@intel.com, arjanv@redhat.com (Arjan van de Ven),
        linux-kernel@vger.kernel.org, linux-ia64@linuxia64.org,
        marcelo@conectiva.com.br, davem@redhat.com, davidm@hpl.hp.com
Subject: Re: [Linux-ia64] patch to no longer use ia64's software mmu
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>>>>> On Tue, 4 Dec 2001 17:18:17 +0000 (GMT), Alan Cox <alan@lxorguk.ukuu.org.uk> said:

  >> I think the issue at hand is whether, longer term, it is
  >> desirable to move all bounce buffer handling into the PCI DMA
  >> layer or whether Linux should continue to make bounce buffer
  >> management visible to drivers.  I'd be interested in hearing
  >> opinions.

  Alan> I think the performance figures we see currently answer that
  Alan> already.

The numbers I have seen so far don't make this obvious.  Tony Luck
reports 95Mbps with a CPU load of 20% after a fixing a performance bug
in the software I/O TLB.  Arjan reported the same 95Mbps figure with
the highmem approach.  Arjan didn't report the CPU load and neither
Tony nor Arjan specified the test environment they were using.

  Alan> IA64 also needs to correct its GFP_DMA to mean "low 16Mb" for
  Alan> ISA DMA. While there is no ISA DMA on ia64 (thankfully) many
  Alan> PCI cards have 26-31 bit limits.

We could do this if we there was a GFP_4GB zone.  Now that 2.5 is open
for business, it won't be long, right?

	--david
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