Messages in this thread | | | Date | Tue, 20 Nov 2007 05:29:29 +0100 | From | Willy Tarreau <> | Subject | Re: CONFIG_IRQBALANCE for 64-bit x86 ? |
| |
On Tue, Nov 20, 2007 at 03:17:15PM +1100, Nick Piggin wrote: > On Tuesday 20 November 2007 15:12, Mark Lord wrote: > > 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 ? > > For that matter, I'd like to know why it has been decided that the > best place for IRQ balancing is in userspace. It should be in kernel > IMO, and it would probably allow better power saving, performance, > fairness, etc. if it were to be integrated with the task balancer as > well.
Agreed. When userspace has something to do with the way IRQs are delivered, it's going to smell as bad as micro-kernels...
Willy
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |