From: "Hong H. Pham" <hong.pham@xxxxxxxxxxxxx> Date: Wed, 3 Jun 2009 12:41:02 -0400 > irq_choose_cpu() should compare the affinity mask against cpu_online_map > rather than CPU_MASK_ALL, since irq_select_affinity() sets the interrupt's > affinity mask to cpu_online_map "and" CPU_MASK_ALL (which ends up being > just cpu_online_map). The mask comparison in irq_choose_cpu() will always > fail since the two masks are not the same. So the CPU chosen is the first CPU > in the intersection of cpu_online_map and CPU_MASK_ALL, which is always CPU0. > That means all interrupts are reassigned to CPU0... > > Distributing interrupts to CPUs in a linearly increasing round robin fashion > is not optimal for the UltraSPARC T1/T2. Also, the irq_rover in > irq_choose_cpu() causes an interrupt to be assigned to a different > processor each time the interrupt is allocated and released. This may lead > to an unbalanced distribution over time. > > A static mapping of interrupts to processors is done to optimize and balance > interrupt distribution. For the T1/T2, interrupts are spread to different > cores first, and then to strands within a core. > > The following is some benchmarks showing the effects of interrupt > distribution on a T2. The test was done with iperf using a pair of T5220 > boxes, each with a 10GBe NIU (XAUI) connected back to back. > > TCP | Stock Linear RR IRQ Optimized IRQ > Streams | 2.6.30-rc5 Distribution Distribution > | GBits/sec GBits/sec GBits/sec > --------+----------------------------------------- > 1 0.839 0.862 0.868 > 8 1.16 4.96 5.88 > 16 1.15 6.40 8.04 > 100 1.09 7.28 8.68 > > Signed-off-by: Hong H. Pham <hong.pham@xxxxxxxxxxxxx> Applied to sparc-next-2.6, thanks a lot! WRT. the NIU interrupt bug, I'm still thinking about how to make further progress on that one. I'll post a followup soon. -- To unsubscribe from this list: send the line "unsubscribe sparclinux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
