linux-kernel - Re: Updated scalable urandom patchkit

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Date:	Tue, 13 Oct 2015 18:20:44 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Theodore Ts'o <tytso@....edu>, George Spelvin <linux@...izon.com>,
	ahferroin7@...il.com, andi@...stfloor.org, jepler@...ythonic.net,
	linux-kernel@...r.kernel.org, linux@...musvillemoes.dk
Subject: Re: Updated scalable urandom patchkit

I tested the two proposed patches from earlier this thread on a 4S
system. This was just with my (worst case) micro.

Unfortunately both patches scale much worse than the duplicated pools,
and can be even worse than the baseline (not sure why).

The base line peaks at slightly above 200K ops/s with less than 20 CPUs.
And the it gets slower until settling around 100K ops/s with more CPUs.

Ted's patch peaks at 350K with four CPUs, but then quickly degrades to
50K ops/s at 20+ CPUs. At 144 CPUs it is slightly faster again at ~80K.

Spelvin's patch peaks at only 140K at 2 CPUs (so it's slower than base line),
stays around 120K upto 20, then degrades quickly to 50K and then slowly
improves again to ~80K.

The duplicated pool patch is ~200K upto 20 CPus, 400K upto 40, 600K at
slightly below 60 CPUs, and then very slowly degrades to 520K at 144. 

-Andi

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