On Tue, 20 Nov 2007 15:17:15 +1100
Nick Piggin <[email protected]> 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?
because the in-kernel one is actually quite bad.
> > 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).
please run the userspace irq balancer, see http://www.irqbalance.org
afaik most distros ship that by default anyway.
> > As near as I can tell, when IRQBALANCE is not configured,
> > all I/O device interrupts go to CPU#0.
that depends on your chipset; some chipsets do worse than that.
>
> > 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.
actually.... no. IRQ balancing is not a "fast" decision; every time you
move an interrupt around, you end up causing a really a TON of cache
line bounces, and generally really bad performance (esp if you do it
for networking ones, since you destroy the packet reassembly stuff in
the tcp/ip stack).
Instead, what ends up working is if you do high level categories of
interrupt classes and balance within those (so that no 2 networking
irqs are on the same core/package unless you have more nics than cores)
etc. Balancing on a 10 second scale seems to work quite well; no need
to pull that complexity into the kernel....
--
If you want to reach me at my work email, use [email protected]
For development, discussion and tips for power savings,
visit http://www.lesswatts.org
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
