From: Grant Grundler <grundler@cup.hp.com>
To: Matthew Wilcox <matthew@wil.cx>
Cc: parisc-linux@thepuffingroup.com
Subject: Re: [parisc-linux] ZONE_DMA
Date: Mon, 01 Jan 2001 22:46:58 -0800 [thread overview]
Message-ID: <200101020647.WAA26293@milano.cup.hp.com> (raw)
In-Reply-To: Your message of "Tue, 02 Jan 2001 01:21:22 PST." <20010102012122.A10153@parcelfarce.linux.theplanet.co.uk>
Matthew Wilcox wrote:
> But, if possible, we want to avoid doing DAC as it cuts down the bandwidth
> (and increases latency by a clock). obviously, if it's a 64-bit device
> and a 64-bit controller, there's no problem, but we should try to stick
> to 32-bit bus addresses where possible.
That's correct. But then we can bypass the I/O MMU. SBA HW has bits
to support that - but I don't fully understand all the limitations of when
this "mode" can be used. Bypassing the I/O MMU would improve DMA performance
and reduce work CPU has to do to "map" each page of DMA.
Though it's generally a good direction, optimizing the PCI bus isn't
always the right answer. Ie moving from 32- to 64-bit wide data
transfers is a *much* bigger performance win than DAC.
grant
Grant Grundler
Unix Systems Enablement Lab
+1.408.447.7253
prev parent reply other threads:[~2001-01-02 6:42 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2001-01-01 17:43 [parisc-linux] ZONE_DMA Matthew Wilcox
2001-01-01 18:09 ` Alan Cox
2001-01-01 18:24 ` Matthew Wilcox
2001-01-01 18:32 ` Alan Cox
2001-01-01 18:55 ` Matthew Wilcox
2001-01-01 19:01 ` Alan Cox
2001-01-01 19:18 ` Matthew Wilcox
2001-01-02 0:59 ` Grant Grundler
2001-01-02 1:21 ` Matthew Wilcox
2001-01-02 6:46 ` Grant Grundler [this message]
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