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Linux Tuning Parameters

Keeping in mind I use ATS Traffic Server in a low-traffic environment, here are the sysctl parameters I've found useful.

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The first two settings are Linux's default socket buffer sizes.  I've found setting this to roughly my "average object size" as reported by "traffic_top" has helped significantly.  For me that value is 48K64K.

The next two settings are Linux's maximum socket buffer size.  I've found setting this relative to my client's link speed has helped.  For me, the link speed is 50Mbps, thus 2MB works out pretty well.

The next two settings specify how Linux handles dynamic IPv4 TCP/IP socket buffer sizes.  I simply reused my settings from above without changing the minimum.

The final setting two settings specifies how Linux optimizes the IPv4 TCP/IP stack.  I found the default, which specifies throughput and NOT latency, to really cause me problems.

I honestly don't know how well this scalesthese two last settings scale, but I'll bet it does they do okay.  I found this setting helped tremendously on a datacenter-grade link.

net.core.rmem_default=4915298304
net.core.wmem_default=4915298304
net.core.rmem_max=2097152
net.core.wmem_max=2097152
net.ipv4.tcp_rmem=4096 4915298304 2097152
net.ipv4.tcp_wmem=4096 4915298304 2097152
net.ipv4.tcp_low_latency=1
net.ipv4.tcp_slow_start_after_idle=0

That's it!  One should probably restart ATS just to be on the safe side, but once these settings are activated they take effect immediately.

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