Date: Sun, 13 Oct 2002 19:26:18 -0700 From: Wes Peters <wes@softweyr.com> To: "M. Warner Losh" <imp@bsdimp.com> Cc: ticso@cicely.de, ticso@cicely8.cicely.de, hch@infradead.org, dillon@apollo.backplane.com, vova@sw.ru, nate@root.org, arch@FreeBSD.org Subject: Re: Database indexes and ram Message-ID: <3DAA2B4A.477A6BBE@softweyr.com> References: <20021012135245.A16453@infradead.org> <20021012.150616.129769790.imp@bsdimp.com> <20021013103538.GG17920@cicely8.cicely.de> <20021013.060648.93373269.imp@bsdimp.com>
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"M. Warner Losh" wrote:
>
> In message: <20021013103538.GG17920@cicely8.cicely.de>
> Bernd Walter <ticso@cicely8.cicely.de> writes:
> : On Sat, Oct 12, 2002 at 03:06:16PM -0600, M. Warner Losh wrote:
> : > In message: <20021012135245.A16453@infradead.org>
> : > Christoph Hellwig <hch@infradead.org> writes:
> : > : On Wed, Oct 09, 2002 at 04:57:37PM -0700, Wes Peters wrote:
> : > : > Linux solved this problem by refusing to do it. The candidates for DMA
> : > : > transfers include skbufs and buffers from the disk buffer pool, both of
> : > : > which are allocated from the lowest 4GB of physical ram when using PAE
> : > : > mode.
> : > :
> : > : Umm, Linux _does_ DMA into any memory if the NIC/HBA/whatever supports
> : > : it.
> : >
> : > Unless the card is 64bit, it can't DMA past 4G.
> :
> : Shouldn't all modern pci chips support two 32bit word addresses.
>
> I don't think so. There's only 32-bits on the bus for the address on
> most pci cards (not the 64-bit pci cards, which are special), so I
> don't see how they can go above 4G. Unless I'm being unusually dense
> this morning.
The PCI spec has a feature for doing two address word transfers so 32-bit
cards can DMA/address 64-bit memory regions, but few if any chipsets support
it.
--
"Where am I, and what am I doing in this handbasket?"
Wes Peters Softweyr LLC
wes@softweyr.com http://softweyr.com/
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