Thanks, it's almost clear now - one more thing. There seems to be 8 columns
in this table. Let's say the lowest 9 bits of my hash are 8 decimal
For 8 the table reads
8: 8 9 10 11 12 13 0 1
The value 8 is an index into a table that yields a row - which of those
cores would be used? The packet could you go a core 8 or 9 or 12?
On Wed, Nov 22, 2017 at 5:55 PM, Alexander Duyck <alexander.du...@gmail.com>
wrote:
> Comments inline below.
>
> On Wed, Nov 22, 2017 at 8:23 AM, Michał Purzyński
> <michalpurzyns...@gmail.com> wrote:
> > Hello!
> >
> > How do I read the indirection table, then one that can be shown with
> > ethtool -x? What is the meaning of columns vs rows and what those numbers
> > are trying to tell me? I'm guessing it's kind of like a weight, but I'm
> not
> > sure how to understand it.
>
> So what the indirection table does is allow us to map bits from the
> RSS hash onto specific rings.
>
> So in the example you provided below there are 512 entries, this
> represents 9 bits. Those 9 bits appear to be mapped onto 14 queues
> based on the table you provided.
>
> So the easiest way to examine this would be to look at skb->hash that
> is being reported by the device in the case of flow director/ATR being
> disabled. What you should find is that if you mask the skb->hash by
> masking it with 511 (0x1FF) what you should find is that the number
> returned will give you the index into this table, and the packet
> itself should be received on the queue associated with that index.
>
> > RX flow hash indirection table for p3p1 with 14 RX ring(s):
> >
> > 0: 0 1 2 3 4 5 6 7
> > 8: 8 9 10 11 12 13 0 1
> > 16: 2 3 4 5 6 7 8 9
> > 24: 10 11 12 13 0 1 2 3
> > 32: 4 5 6 7 8 9 10 11
> > 40: 12 13 0 1 2 3 4 5
> > 48: 6 7 8 9 10 11 12 13
> > 56: 0 1 2 3 4 5 6 7
> > 64: 8 9 10 11 12 13 0 1
> > 72: 2 3 4 5 6 7 8 9
> > 80: 10 11 12 13 0 1 2 3
> > 88: 4 5 6 7 8 9 10 11
> > 96: 12 13 0 1 2 3 4 5
> > 104: 6 7 8 9 10 11 12 13
> > 112: 0 1 2 3 4 5 6 7
> > 120: 8 9 10 11 12 13 0 1
> > 128: 2 3 4 5 6 7 8 9
> > 136: 10 11 12 13 0 1 2 3
> > 144: 4 5 6 7 8 9 10 11
> > 152: 12 13 0 1 2 3 4 5
> > 160: 6 7 8 9 10 11 12 13
> > 168: 0 1 2 3 4 5 6 7
> > 176: 8 9 10 11 12 13 0 1
> > 184: 2 3 4 5 6 7 8 9
> > 192: 10 11 12 13 0 1 2 3
> > 200: 4 5 6 7 8 9 10 11
> > 208: 12 13 0 1 2 3 4 5
> > 216: 6 7 8 9 10 11 12 13
> > 224: 0 1 2 3 4 5 6 7
> > 232: 8 9 10 11 12 13 0 1
> > 240: 2 3 4 5 6 7 8 9
> > 248: 10 11 12 13 0 1 2 3
> > 256: 4 5 6 7 8 9 10 11
> > 264: 12 13 0 1 2 3 4 5
> > 272: 6 7 8 9 10 11 12 13
> > 280: 0 1 2 3 4 5 6 7
> > 288: 8 9 10 11 12 13 0 1
> > 296: 2 3 4 5 6 7 8 9
> > 304: 10 11 12 13 0 1 2 3
> > 312: 4 5 6 7 8 9 10 11
> > 320: 12 13 0 1 2 3 4 5
> > 328: 6 7 8 9 10 11 12 13
> > 336: 0 1 2 3 4 5 6 7
> > 344: 8 9 10 11 12 13 0 1
> > 352: 2 3 4 5 6 7 8 9
> > 360: 10 11 12 13 0 1 2 3
> > 368: 4 5 6 7 8 9 10 11
> > 376: 12 13 0 1 2 3 4 5
> > 384: 6 7 8 9 10 11 12 13
> > 392: 0 1 2 3 4 5 6 7
> > 400: 8 9 10 11 12 13 0 1
> > 408: 2 3 4 5 6 7 8 9
> > 416: 10 11 12 13 0 1 2 3
> > 424: 4 5 6 7 8 9 10 11
> > 432: 12 13 0 1 2 3 4 5
> > 440: 6 7 8 9 10 11 12 13
> > 448: 0 1 2 3 4 5 6 7
> > 456: 8 9 10 11 12 13 0 1
> > 464: 2 3 4 5 6 7 8 9
> > 472: 10 11 12 13 0 1 2 3
> > 480: 4 5 6 7 8 9 10 11
> > 488: 12 13 0 1 2 3 4 5
> > 496: 6 7 8 9 10 11 12 13
> > 504: 0 1 2 3 4 5 6 7
>
> So for example if I had an RSS hash that was something like 0x01234567
> and I masked the lower 9 bits I would get 0x167, which comes out as
> 359 decimal. As such I would expect the packet to be received on queue
> 9 based on the table provided here.
>
> I hope that helps to clarify how the indirection table is used.
>
> - Alex
>
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