[ovs-discuss] max mega flow 64k per pmd or per dpcls?

Hui Xiang xianghuir at gmail.com
Fri Jun 30 01:55:23 UTC 2017


Thanks Bodireddy.

Sorry I am a bit confused about the EMC occupied size per PMD, here[1] has
a different story.

Do you mean in real scenarios OVS-DPDK can be memory bound on EMC? I
thought EMC should be totally fit in LLC.

If the megaflows just part in LLC, then the cost of copy between memory and
LLC should be large, isn't it not like what defined as 'fast path' in
userspace compared with kernel datapath? And if most of megaflows are in
memory, the reason of every PMD  has one dpcls instance is to follow the
rule PMD thread should has local data as most as it can, but not every PMD
put it in its local cache, if that is true, I can't see why 64k is the
limit num, unless this is an experience best value calculated from
vtune/perf resutls.

You are probably enabled hyper-thread with 35MB and got 28 cores.

[1] https://mail.openvswitch.org/pipermail/ovs-dev/2015-May/298999.html



On Thu, Jun 29, 2017 at 10:23 PM, Bodireddy, Bhanuprakash <
bhanuprakash.bodireddy at intel.com> wrote:

> >
> >I guess the answer is now the general LLC is 2.5M per core so that there
> is 64k
> >flows per thread.
>
> AFAIK, the no. of flows here may not have to do anything with LLC.  Also
> there is EMC cache(8k entries) of ~4MB per PMD thread.
> Yes the performance will be nice with simple test cases (P2P with 1 PMD
> thread) as most of this fits in to LLC. But in real scenarios  OvS-DPDK can
> be memory bound.
>
> BTW, on my DUT the LLC is 35MB and has 28 cores and so the assumption of
> 2.5M/core isn't right.
>
> - Bhanuprakash.
>
> >
> >On Fri, Jun 23, 2017 at 11:15 AM, Hui Xiang <xianghuir at gmail.com> wrote:
> >Thanks Darrell,
> >
> >More questions:
> >Why not allocating 64k for each dpcls? does the 64k just fit in L3 cache
> or
> >anywhere? how it is calculated in such an exact number?  If there are more
> >ports added for polling, for avoid competing can I increase the 64k size
> into a
> >bigger one? Thanks.
> >
> >Hui.
> >
> >
>
>
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