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From: Pete Zaitcev <zaitcev@redhat.com>
To: Krzysztof Halasa <khc@pm.waw.pl>
Cc: linux-kernel@vger.kernel.org, Pete Zaitcev <zaitcev@redhat.com>
Subject: Re: [PATCH] RFC: kills consistent_dma_mask
Date: Mon, 18 Aug 2003 11:15:22 -0400	[thread overview]
Message-ID: <20030818111522.A12835@devserv.devel.redhat.com> (raw)
In-Reply-To: <m3oeynykuu.fsf@defiant.pm.waw.pl>; from khc@pm.waw.pl on Mon, Aug 18, 2003 at 12:34:17AM +0200

> From: Krzysztof Halasa <khc@pm.waw.pl>
> Date: 18 Aug 2003 00:34:17 +0200

> It's unneeded (it can be easily done in a driver, should a need arrive,
> without polluting the PCI subsystem) and is not supported by "DMA" API.

Are you talking about doing tripple calls, e.g.

       pci_set_dma_mask(pdev, 0xFFFFFFFF);
       foo = pci_alloc_consistent(pdev, size, &handle);
       // Restore for upcoming streaming allocations
       pci_set_dma_mask(pdev, 0xFFFFFFFFFFFFFFFF);

Possibly Jes considered that alternative and decided that it
did not allow for sufficient performance.

> It isn't even implemented on most platforms - only x86_64 and ia64 have
> support for it, while on the remaining archs using it according to the
> docs (with non-default value) could mean Oops or something like that.

Before you go for that, I'd rather see you implementing the
double/tripple calls in drivers, check for effects, THEN
go for removal of the mask. If you cannot do it, plea SGI people
to test it on SN-2 for you (or same for Intel Tiger box).

> This patch doesn't actually change any current kernel behaviour.

Sure it does. It blows all non-mmu ia64 out of the water.

The consistent mask looks a little distasteful to me, and I think
it should not buy us performance because consistent allocations
are not supposed to be fast. They are bad, but what you are doing
is worse: you are trying to ruin the day of legitimate users.
Please, be reasonable. Get SGI buy-in and come back.

-- Pete

  parent reply	other threads:[~2003-08-18 15:15 UTC|newest]

Thread overview: 46+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2003-08-17 22:34 [PATCH] RFC: kills consistent_dma_mask Krzysztof Halasa
2003-08-18  6:37 ` David S. Miller
2003-08-18 12:44   ` Krzysztof Halasa
2003-08-18 12:43     ` David S. Miller
2003-08-18 15:54       ` Krzysztof Halasa
2003-08-18 16:49         ` David S. Miller
2003-08-18 18:21           ` Krzysztof Halasa
2003-08-18 18:50             ` David S. Miller
2003-08-18 21:58               ` Krzysztof Halasa
2003-08-19  9:24                 ` Jes Sorensen
2003-08-19  9:21         ` Jes Sorensen
2003-08-18 13:00     ` Jes Sorensen
2003-08-18  8:07 ` Christoph Hellwig
2003-08-18 15:15 ` Pete Zaitcev [this message]
2003-08-18 16:14   ` Krzysztof Halasa
2003-08-19  9:16     ` Jes Sorensen
2003-08-19  9:49       ` Krzysztof Halasa
2003-08-19 10:15         ` Jes Sorensen
2003-08-19  9:03   ` Jes Sorensen
2003-08-19 13:07     ` Alan Cox
2003-08-19 13:20       ` Jes Sorensen
2003-08-19 16:55       ` David S. Miller
2003-08-19 18:33         ` Alan Cox
2003-08-19 18:31           ` David S. Miller
2003-08-19 20:31         ` Krzysztof Halasa
2003-08-22 11:54           ` Krzysztof Halasa
2003-08-23 17:11             ` Jes Sorensen
2003-08-24 12:06               ` Krzysztof Halasa
2003-08-24 13:00                 ` David S. Miller
2003-08-24 19:58                   ` Krzysztof Halasa
2003-08-25  8:50                     ` Jes Sorensen
2003-08-30 21:18                     ` Krzysztof Halasa
2003-08-31  1:50                       ` David S. Miller
2003-08-31 12:52                         ` Alan Cox
2003-08-31 15:24                           ` Krzysztof Halasa
2003-09-01  5:22                           ` David S. Miller
2003-09-01  7:34                             ` Krzysztof Halasa
2003-09-01  7:43                               ` David S. Miller
2003-09-01 17:14                                 ` Krzysztof Halasa
2003-09-01 17:28                                   ` David S. Miller
2003-09-01 18:24                                     ` Krzysztof Halasa
2003-09-01  7:54                             ` Alan Cox
2003-09-01  7:52                               ` David S. Miller
2003-09-01 16:27                                 ` Krzysztof Halasa
2003-09-01 17:33                                   ` David S. Miller
2003-08-25  8:47                 ` Jes Sorensen

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