Re: [dpdk-users] Bigger mempool leads to worst performances.

Re: [dpdk-users] Bigger mempool leads to worst performances.

[Benoit Ganne (bganne)]

> It looks like that in our environment increasing the mempool reduce the
> capture performance, any suggestion on what I might look at to
> troubleshoot the problem? Apparently we can't go beyond 4GiB mempool
> without performance penalties.
> (Please note that 1GiB hugepage are configured to serve all the require
> additional memory.)

I'd bet it on page walks because of TLB misses: if I am not mistaken, on Intel you only have 4 TLB entries for 1GB hugepages, and prior to Skylake you have no victim cache. So, as soon as you use more than 4 x 1GB hugepages, you'll start triggering page walks because all your pages do no longer fit in the TLB.
You should be able to check that with 'perf stat -e dTLB-loads,dTLB-load-misses,dTLB-stores,dTLB-store-misses -a -I1000' or similar.

Best
ben

[dpdk-users] Bigger mempool leads to worst performances.

[Filip Janiszewski]

Hi All,

I'm very aware the question is generic, but we can't really understand
what would be the problem here..

In short, we've a capture software running smoothly at 20GbE and
capturing everything, recently we've switched gear and increased the
amount of data, and encountered some drops.

One of the first ideas was that increasing the mempool for the port
would lead to some performance benefit or worst case scenario to no
change in the drop rate, but, unexpectedly we started dropping
*substantially more* packets..

It looks like that in our environment increasing the mempool reduce the
capture performance, any suggestion on what I might look at to
troubleshoot the problem? Apparently we can't go beyond 4GiB mempool
without performance penalties.

(Please note that 1GiB hugepage are configured to serve all the require
additional memory.)

Thanks

-- 
BR, Filip
+48 666 369 823