OpenSSL 1.1.1g Windows build slow rsa tests

[Jan Just Keijser]

Hi Dan,

On 21/01/21 19:22, Dan Heinz wrote:
> [...]

> Thank you all for the helpful suggestions. When I removed no-asm and 
> built using nmake in the Developer Command Prompt for Visual Studio 
> 2015, I ended up getting an error "VC-WIN64A X86 conflicts with target 
> x64". From the command prompt I ran cl and saw this "Microsoft (R) 
> C/C++ Optimizing Compiler Version 19.00.24215.1 for x86". So I was 
> building for x86? I'm not sure why it built with no-asm, but it did.
> Once I ran the correct command prompt (I used Visual Studio x64 Native Tools Command Prompt), I saw a huge speed increase.  For example, 2048 bits:
> Doing 2048 bits private rsa's for 10s: 8384 2048 bits private RSA's in 10.02s
> Doing 2048 bits public rsa's for 10s: 236090 2048 bits public RSA's in 9.98s
>
> Previously, I saw:
> Doing 2048 bits private rsa's for 10s: 409 2048 bits private RSA's in 10.00s
> Doing 2048 bits public rsa's for 10s: 15663 2048 bits public RSA's in 10.02s
>
> For further testing, I added back no-asm and my speed tests were in line with the downloaded openssl binary I was testing with.
> Doing 2048 bits private rsa's for 10s: 1868 2048 bits private RSA's in 10.00s
> Doing 2048 bits public rsa's for 10s: 71338 2048 bits public RSA's in 10.02s
>
> You can see removing no-asm does make a pretty large speed increase too.
>
> In summary, using the correct build tools helps (although I am surprised it built with no-asm).  And removing no-asm sped things up.

Not sure why you'd want to do a 'no-asm' build to begin with, but 
another thing worth testing with your "asm" build is to run the speed 
test like this:
  set OPENSSL_ia32cap=0
  openssl speed rsa
(Linux/UNIX:  OPENSSL_ia32cap=0 openssl speed rsa)

On my (10th gen Intel ) laptop this gives me a ~35% performance hit. 
Explanation:
- no-asm build -> compiler generates all code, no hand-tuned assembly 
used at all; should be slowest

- asm build + OPENSSL_ia32cap=0  -> no newer CPU features used, but 
hand-tuned assembly is used. Especially AES encryption takes a hit if 
you disable these newer features

- asm build -> hand-tuned assemby, including the use of all new CPU 
features such as AES, SHA etc.

I've found that this sometimes helps manage expectations when the "build 
environment" CPU and the "runtime environment" CPU are very different. 
I've seen a developer claim his/her code runs blazingly fast on his/her 
Core i7 bla bla but when deploying it on a cheaper runtime device 
performance is terrible.

Note that no-asm + OPENSSL_ia32cap=0 should not have any effect compared 
to "no-asm".

JM2CW,

JJK / Jan Just Keijser