title: linux irq affinity set cannot take effctive
body: <p>when i set irq for my Ethernet cannot be effective. (irq from 99-119)</p>
  
  <pre><code>$ sudo cat /proc/irq/109/smp_affinity
  00,00000400
  $ sudo sh -c "echo 0 &gt; /proc/irq/109/smp_affinity"
  $ sudo cat /proc/irq/109/smp_affinity
  00,00000400
  </code></pre>
  
  <p>i want to set all ethernet irq to bind with cpu0. but no lucky for me to set it. i am not sure what kind of problems i met. 
  and i noticed affinity_hint has following value, and i cannot set it anyway. </p>
  
  <pre><code>$sudo cat /proc/irq/109/affinity_hint 
  00,00000400
  $ sudo sh -c "echo 0 &gt; /proc/irq/109/affinity_hint"
  sh: line 0: echo: write error: Input/output error
  </code></pre>
  
  <p>this system i have 2 cpus with 6 cores. and enable hyper thread. totally has 24 cpu cores. </p>
  
  <pre><code>Architecture:          x86_64
  CPU op-mode(s):        32-bit, 64-bit
  Byte Order:            Little Endian
  CPU(s):                40
  On-line CPU(s) list:   0-39
  Thread(s) per core:    2
  Core(s) per socket:    10
  Socket(s):             2
  NUMA node(s):          2
  Vendor ID:             GenuineIntel
  CPU family:            6
  Model:                 62
  Model name:            Intel(R) Xeon(R) CPU E5-2660 v2 @ 2.20GHz
  Stepping:              4
  CPU MHz:               1201.921
  BogoMIPS:              4404.51
  Virtualization:        VT-x
  L1d cache:             32K
  L1i cache:             32K
  L2 cache:              256K
  L3 cache:              25600K
  NUMA node0 CPU(s):     0-9,20-29
  NUMA node1 CPU(s):     10-19,30-39
  </code></pre>
  
  <p>please help advise how to resolve. thanks!</p>