From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Mosberger Date: Mon, 03 Dec 2001 21:47:41 +0000 Subject: Re: [Linux-ia64] patch to no longer use ia64's software mmu Message-Id: List-Id: References: In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-ia64@vger.kernel.org Arjan> Hi, The patch below (against 2.4.16) makes the ia64 port no Arjan> longer use the (VERY slow) software IO mmu but makes it use Arjan> the same mechanism the x86 PAE port uses: it lets the higher Arjan> layers take care of the proper bouncing of PCI-unreachable Arjan> memory. The implemenation is pretty simple; instead of having Arjan> a 4Gb GFP_DMA zone and a GFP_KERNEL zone, the Arjan> ia64 port now has a 4Gb GFP_DMA zone and a Arjan> GFP_HIGH zone. Since the ia64 cpu can address all of this Arjan> memory directly, the kmap() and related functions are Arjan> basically nops. Arjan> The result: 100 mbit ethernet performance on a ia64 machine Arjan> with 32Gb of ram increased more than 4x (from 20 mbit to 95 Arjan> mbit).... Arjan> The only downside is that the current kernel will always Arjan> bounce buffer disk IO even if the scsi card is 64 bit PCI Arjan> capable; Jens Axboe's block highmem patch fixes that downside Arjan> nicely though. How soon will Jens' patch make it into the official tree? I think that would be a pre-requisite before switching to a highmem based implementation. Another concern I have is that, fundamentally, I dislike the idea of penalizing all IA-64 platforms due to one chipset that is, shall we say, "lacking" (i.e., doesn't have an I/O TLB). Could someone comment on whether the 870 will have I/O TLB support (private mail is fine, if you don't feel comfortable sending mail to all the lists...). Thanks, --david