Messages in this thread |  | | Date | Fri, 9 Feb 2001 17:56:06 -0500 (EST) | From | Donald Becker <> | Subject | Re: [PATCH] starfire reads irq before pci_enable_device. |
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On 9 Feb 2001, Jes Sorensen wrote:
> >>>>> "Jeff" == Jeff Garzik <jgarzik@mandrakesoft.com> writes: > Jeff> Donald Becker wrote: > >> On Tue, 16 Jan 2001, Jeff Garzik wrote: > * IA64 support (Jes) Oh, > >> and this is completely bogus. This isn't a fix, it's a hack that > >> covers up the real problem. > >> > >> The align-copy should *never* be required because the alignment > >> differs between DIX and E-II encapsulated packets. The machine > >> shouldn't crash because someone sends you a different encapsulation > >> type! > > The ia64 kernel has gotten mis aligned load support, but it's slow as > a dog so we really want to copy the packet every time anyway when the > header is not aligned. If people send out 802.3 headers or other crap > on Ethernet then it's just too bad.
Note the word "required", meaning "must be done" vs. "recommended" meaning "should be done".
The initial issue was a comment in a starfire patch that claimed an IA64 bug had been fixed. The copy breakpoint change might have improved performance by doing a copy-align, but it didn't fix a bug.
That performance tradeoff was already anticipated: the 'rx_copybreak' value that was changed was a module parameter, not a constant. That allows a module-load-time tradeoff, based the specific implementation, of copying the received packet or accepting a few unaligned loads of the usually small IP header. See the comments in starfire.c, as well as several other bus-master drivers.
Donald Becker becker@scyld.com Scyld Computing Corporation http://www.scyld.com 410 Severn Ave. Suite 210 Second Generation Beowulf Clusters Annapolis MD 21403 410-990-9993
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