phc-discussions - Re: [PHC] Lyra2 initial review

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Date: Thu, 17 Apr 2014 20:39:41 +0400
From: Solar Designer <solar@...nwall.com>
To: discussions@...sword-hashing.net
Subject: Re: [PHC] Lyra2 initial review

Bill,

How did you convert the "time" output to peak GiB/s?  I tried
double-checking your results, and I am getting different numbers.

Did you include the memory allocation overhead time or not?  I guess you
did, which is a reason why faster schemes (those filling 2 GiB sooner)
would appear to use less bandwidth (they'd spend _relatively_ more time
on memory allocation overhead).  Anyhow, I failed to confirm your
results, whether with this assumption or not.

On Thu, Apr 17, 2014 at 11:08:25AM -0400, Bill Cox wrote:
> *********** Lyra2 - no modifications, hashing 2GiB of memory
[...]
> real    0m1.320s
> user    0m1.200s
> sys     0m0.110s

2/1.320 = 1.52 GiB/s
2/1.200 = 1.67 GiB/s

> *********** Yescript - 5 of 6 calls to PWXFORM_ROUND commented out, and 3
> of 4 calls to SALSA20_2ROUNDS
[...]
> real    0m0.709s
> user    0m0.560s
> sys     0m0.140s

2/0.709 = 2.82 GiB/s
2/0.560 = 3.57 GiB/s

> *********** TwoCats - multiples was set to 1, and #threads set to 1
[...]
> real    0m0.431s
> user    0m0.330s
> sys     0m0.080s

2/0.431 = 4.64 GiB/s
2/0.330 = 6.06 GiB/s

> Lyra2:
> Peak memory/second: 1.63 GiB/s
[...]

> Yescript:
> Peak memory/second: 3.03 GiB/s
[...]

> TwoCats:
> Peak memory/second: 4.98 GiB/s
[...]

These don't match any of the above, as you can see.  Oh, I think I
figured it out: you meant GB/s, but mistyped GiB/s.  Right?  e.g.:

2/0.431*2^30/10^9 = 4.98 GB/s

And the memory allocation overhead is a reason why Lyra2, with its
higher number of r/w per location, appears faster in terms of memory
bandwidth usage.  (Not necessarily the only reason.)

Alexander