Thomas Lendacky <tahm@xxxxxxxxxxxxxxxxxx> writes:
> I ran some TCP_RR and TCP_STREAM sessions, both host-to-guest and
> guest-to-host, with a form of the histogram patch applied against a
> RHEL6.3 kernel. The histogram values were reset after each test.
Hey, thanks! This is exactly what I wanted to see...
> 60 session TCP_RR from host-to-guest with 256 byte request and 256 byte
> response for 60 seconds:
>
> Queue histogram for virtio1:
> Size distribution for input (max=7818456):
> 1: 7818456 ################################################################
These are always 1, so we don't indirect them anyway, so no cache required.
> Size distribution for output (max=7816698):
> 2: 149
> 3: 7816698 ################################################################
> 4: 2
> 5: 1
> Size distribution for control (max=1):
> 0: 0
OK, tiny TCP data, but latency sensitive.
> Queue histogram for virtio1:
> Size distribution for input (max=16050941):
> 1: 16050941 ################################################################
> Size distribution for output (max=1877796):
> 2: 1877796 ################################################################
> 3: 5
> Size distribution for control (max=1):
> 0: 0
Acks. Not that many, not that latency sensitive.
> 4 session TCP_STREAM from guest-to-host with 4K message size for 60 seconds:
>
> Queue histogram for virtio1:
> Size distribution for input (max=1316069):
> 1: 1316069 ################################################################
> Size distribution for output (max=879213):
> 2: 24
> 3: 24097 #
> 4: 23176 #
> 5: 3412
> 6: 4446
> 7: 4663
> 8: 4195
> 9: 3772
> 10: 3388
> 11: 3666
> 12: 2885
> 13: 2759
> 14: 2997
> 15: 3060
> 16: 2651
> 17: 2235
> 18: 92721 ######
> 19: 879213 ################################################################
Hey, that +1 is there in MAX_SKB_FRAGS for a reason! Who knew?
This looks like we could really use a:
int vq_set_indirect_cache(struct virtqueue *vq, unsigned num);
Which networking would set on the xmit queue(s) if we have GSO.
The real question is now whether we'd want a separate indirect cache for
the 3 case (so num above should be a bitmap?), or reuse the same one, or
not use it at all?
Benchmarking will tell...
Thanks,
Rusty.
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