Subject: Re: [PATCH] RPS: Sparse connection optimizations

From: Deng-Cheng Zhu <[email-masked]>
Date: Wed, 2 May 2012 12:16:39 +0800

On 05/02/2012 12:12 PM, Eric Dumazet wrote:
> On Wed, 2012-05-02 at 12:08 +0800, Deng-Cheng Zhu wrote:
>
>> Unfortunately, on the Malta platform, NIC irqs are not suitable for SMP
>> IRQ affinity -- they are based on XT-PIC. However, I did do some RPS
>> tests where different CPU masks were assigned to the 2 NICs. And the
>> throughput *WAS* better than that of assigning the same mask to NICs.
>> But the problem addressed in this patch *STILL* exists -- hash indexing
>> causes imbalance across CPUs in the case of sparse connections.
>
> You mean your two NIC irqs are handled by CPU0 and this cant be
> changed ?
>
> That really is bad.
>
>
>

Yes, that's right. It's not IO-APIC enabled. When trying to write values
to /proc/irq/$irqnum/smp_affinity:

echo: write error: Input/output error

Deng-Cheng