From: "Feldman, Scott" <scott.feldman@intel.com>
To: "David Gibson" <dwg@au1.ibm.com>
Cc: <linux-kernel@vger.kernel.org>,
"Anton Blanchard" <anton@samba.org>,
"Nancy Milliner" <milliner@us.ibm.com>,
"Herman Dierks" <hdierks@us.ibm.com>,
"Ricardo Gonzalez" <ricardoz@us.ibm.com>
Subject: RE: e1000 performance hack for ppc64 (Power4)
Date: Thu, 12 Jun 2003 18:16:11 -0700 [thread overview]
Message-ID: <C6F5CF431189FA4CBAEC9E7DD5441E010107D932@orsmsx402.jf.intel.com> (raw)
David, arch-specific code in the driver concerns me. I would really
like to avoid any arch-specific code in the driver if at all possible.
Can we find a way to move this work to the arch-dependent areas? This
doesn't seem to be an issue unique to e1000, so moving this up one level
should benefit other devices as well. More questions below.
> Peculiarities in the PCI bridges on Power4 based ppc64 machines mean
> that unaligned DMAs are horribly slow. This hits us hard on gigabit
> transfers, since the packets (starting from the MAC header) are
> usually only 2-byte aligned.
2-byte alignment is bad for ppc64, so what is minimum alignment that is
good? (I hope it's not 2K!) What could you do at a higher level to
present properly aligned buffers to the driver?
> The patch below addresses this by copying and realigning packets into
> nicely 2k aligned buffers. As well as fixing the alignment that
> minimises the number of TCE lookups, and because we allocate the
> buffers pci_alloc_consistent(), we avoid setting up and tearing down
> the TCE mappings for each packet.
If I'm understanding the patch correctly, you're saying unaligned DMA +
TCE lookup is more expensive than a data copy? If we copy the data, we
loss some of the benefits of TSO and Zerocopy and h/w checksum
offloading! What is more expensive, unaligned DMA or TCE?
-scott
next reply other threads:[~2003-06-13 1:02 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-06-13 1:16 Feldman, Scott [this message]
2003-06-13 23:15 ` e1000 performance hack for ppc64 (Power4) Anton Blanchard
-- strict thread matches above, loose matches on Subject: below --
2003-06-16 18:56 Feldman, Scott
2003-06-16 18:21 Feldman, Scott
2003-06-16 18:30 ` Dave Hansen
2003-06-15 14:40 Herman Dierks
2003-06-15 14:44 ` David S. Miller
2003-06-16 16:17 ` Nivedita Singhvi
2003-06-15 14:32 Herman Dierks
2003-06-13 23:52 Feldman, Scott
2003-06-13 23:52 ` David S. Miller
2003-06-14 0:55 ` Anton Blanchard
2003-06-14 1:34 ` David S. Miller
2003-06-14 0:03 ` Anton Blanchard
2003-06-13 22:13 Feldman, Scott
2003-06-13 17:03 Herman Dierks
2003-06-13 15:17 Herman Dierks
2003-06-13 16:21 ` Dave Hansen
2003-06-13 22:38 ` Anton Blanchard
2003-06-13 22:46 ` David S. Miller
2003-06-13 23:18 ` Anton Blanchard
2003-06-14 1:52 ` Lincoln Dale
2003-06-14 5:41 ` David S. Miller
2003-06-14 5:52 ` Lincoln Dale
2003-06-14 6:08 ` David S. Miller
2003-06-14 6:14 ` David S. Miller
2003-06-14 6:27 ` William Lee Irwin III
2003-06-14 17:08 ` Greg KH
2003-06-14 17:19 ` Greg KH
2003-06-14 17:21 ` Riley Williams
2003-06-15 3:01 ` David S. Miller
2003-06-14 5:16 ` Nivedita Singhvi
2003-06-14 5:36 ` David S. Miller
2003-06-12 3:32 David Gibson
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