Re: irqtune: improve serial port performance by 3x?
Hi again..
In my never-ending battle to make the kernel behave well by default without
needing "irqtune" (which is very setup-specific, and as such not something
the kernel can do automatically), I was thinking of doing interrupt priority
rotations instead of the current fixed mode.
Now, doing a rotating interrupt priority means that the priorities
essentially go away completely, which is not the optimal solution (having
high serial line priorities is good, no question about it). However, while
not exactly optimal, it _is_ a fair solution, and likely to be better than
what we currently have.
Rotating priorities should also work reasonably well for multiple serial
interrupt sources, which irqtune doesn't really handle (depending on what the
interrupt numbers are, irqtune can work well, though). Also, unlike irqtune,
there shouldn't be any unfairness toward other devices so it should work well
under wildly different circumstances.
In short, rotating priorities are a reasonable thing to do by default,
and I'd like people who have been trying out "irqtune" (and who actually
see some differences with it) to try out this very simple patch.. How
does this work for you?
(This is actually how Linux/alpha has been handling interrupts from the very
beginning)
Linus
-----
--- v2.0.16/linux/include/asm-i386/irq.h Thu Aug 29 19:15:14 1996
+++ linux/include/asm-i386/irq.h Sun Sep 1 10:53:04 1996
@@ -90,7 +90,7 @@
"outb %al,$0x21\n\t" \
"jmp 1f\n" \
"1:\tjmp 1f\n" \
- "1:\tmovb $0x60+"#nr",%al\n\t" \
+ "1:\tmovb $0xE0+"#nr",%al\n\t" \
"outb %al,$0x20\n\t"
#define ACK_SECOND(mask,nr) \
@@ -102,11 +102,11 @@
"outb %al,$0xA1\n\t" \
"jmp 1f\n" \
"1:\tjmp 1f\n" \
- "1:\tmovb $0x60+"#nr",%al\n\t" \
+ "1:\tmovb $0xE0+"#nr",%al\n\t" \
"outb %al,$0xA0\n\t" \
"jmp 1f\n" \
"1:\tjmp 1f\n" \
- "1:\tmovb $0x62,%al\n\t" \
+ "1:\tmovb $0xE2,%al\n\t" \
"outb %al,$0x20\n\t"
#define UNBLK_FIRST(mask) \
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