Messages in this thread | | | Date | Fri, 14 Nov 2008 19:10:13 -0500 | From | Theodore Tso <> | Subject | Re: [RFC 2/2] serial/8250.c: Use self-adjusting list for port poll order. |
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On Fri, Nov 14, 2008 at 09:47:11PM +0000, Alan Cox wrote: > > This code does that by using the previous poll cycles as a hint. > > If a port is idle, it will migrate to the end of the list and > > only have to be checked once. > > > > Part 1 changed the list to singly-linked to make the list shuffling easier. > > > > Comments? Please? > > Is it really worth the complexity > > - PCI ports are shared IRQ always > - Legacy ports are almost never shared IRQ on the LPC bus (and are > increasingly going away)
It's worth the complexity only *if* you have enough ports shared on a single IRQ and simultaneously such that there a risk that if you don't poll them quickly enough, characters will actually get dropped from the UART's FIFO. The question is whether that is likely to happen on modern CPU's. I worred about such things when I tried to make 16 115kbps serial ports work at full-speed using relatively primitive 16550A UART's with 16 character FIFO's on a 40 MHz 386. But (a) UART's generally have deeper FIFO's these days, and (b) CPU's have gotten a wee bit faster since 1992.
So color me dubious that this is actually necessary....
- Ted
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