CONFIG_IRQBALANCE for 64-bit x86 ?

[Mark Lord <lkml@rtr.ca>]

On 32-bit x86, we have CONFIG_IRQBALANCE available,
but not on 64-bit x86.  Why not?

I ask, because this feature seems almost essential to obtaining
reasonable latencies during heavy I/O with fast devices.

My 32-bit Core2Duo MythTV box drops audio frames without it,
but works perfectly *with* IRQBALANCE.

My QuadCore box works very well in 32-bit mode with IRQBALANCE,
but responsiveness sucks bigtime when run in 64-bit mode (no IRQBALANCE)
during periods of multiple heavy I/O streams (USB flash drives).

That's with both the 32 and 64 bit versions of Kubuntu Gutsy,
so the software uses pretty much identical versions either way.

As near as I can tell, when IRQBALANCE is not configured,
all I/O device interrupts go to CPU#0.

I don't think our CPU scheduler takes that into account when assigning
tasks to CPUs, so anything sent to CPU0 runs with very high latencies.

Or something like that.

Why no IRQ_BALANCE in 64-bit mode ?
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