Messages in this thread | | | Date | Tue, 13 Feb 2001 20:20:35 -0500 (EST) | From | Donald Becker <> | Subject | Re: [PATCH] starfire reads irq before pci_enable_device. |
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On 12 Feb 2001, Jes Sorensen wrote:
> >>>>> "Donald" == Donald Becker <becker@scyld.com> writes: > > Donald> On 9 Feb 2001, Jes Sorensen wrote: > >> 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. > > Donald> Note the word "required", meaning "must be done" > Donald> vs. "recommended" meaning "should be done". > > Donald> The initial issue was a comment in a starfire patch that > Donald> claimed an IA64 bug had been fixed. The copy breakpoint > Donald> change might have improved performance by doing a copy-align, > Donald> but it didn't fix a bug. > > I agree it was a bug, and yes it has been fixed.
There was not a bug in the driver. The bug was/is in the protocol handling code. The protocol handling code *must* be able to handle unaligned IP headers.
> Donald> That performance tradeoff was already anticipated: the > Donald> 'rx_copybreak' value that was changed was a module parameter, .. > In this case it just results in a performance degradation for 99% of > the usage. What about making the change so it is optimized away unless > IPX is enabled?
??? - It's not just IPX hosts that send 802.3 headers. - While a good initial value might depend on the architecture, the best setting is processor implementation and environment dependent. Those details are not known at compile time. - The code path cost of a module option is only a compare and a conditional branch.
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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