Subject: FlameGraph of mlx4 early drop with order-0 pages

From: Jesper Dangaard Brouer <[email-masked]>
Date: Fri, 15 Apr 2016 21:40:34 +0200

Hi Mel,

I did an experiment that you might find interesting.  Using Brenden's
early drop with eBPF in the mxl4 driver.  I changed the mlx4 driver to
use order-0 pages.  It usually use order-3 pages to amortize the cost
of calling the page allocator (which is problematic for other reasons,
like memory pin-down, latency spikes and multi CPU scalability)

With this change I could do around 12Mpps (Mill packet per sec) drops,
usually does 14.5Mpps (limited due to a HW setup/limit, with idle cycles). 

Looking at the perf report as a FlameGraph, the page allocator clearly
show up as the bottleneck: 

http://people.netfilter.org/hawk/FlameGraph/flamegraph-mlx4-order0-pages-eBPF-XDP-drop.svg

Signing off, heading for the plane soon... see you at MM-summit!
-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  Author of http://www.iptv-analyzer.org
  LinkedIn: http://www.linkedin.com/in/brouer

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