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Date: Mon, 7 Sep 2015 21:36:37 +0200
From: magnum <>
Subject: Re: SIMD_PARA_SHA256

On 2015-09-07 11:39, Solar Designer wrote:
> On Mon, Sep 07, 2015 at 09:31:27AM +0200, magnum wrote:
>> On 2015-09-06 21:59, Solar Designer wrote:
>>> We should increase SIMD_PARA_SHA256 from 1 to 2 at least for XOP builds.

>> Perhaps we should do so for SHA-1 too if built without OpenMP (unless
>> that is already the case).
> This is not obvious.  For fast hashes, we currently disable OpenMP and
> suggest use of --fork, and I expect that --fork will show similar
> behavior to OpenMP in terms of which interleaving factors are optimal.
> Maybe we should test --fork=8 explicitly and decide based on that.

You are right of course. It's a pity you can't "--test --fork" yet. I 
only committed the x2 for SHA256 with XOP.

>> Do you have some gcc-4.9 for bull already built that we could try too?
> Not already built, but I can build it easily.  Why 4.9 and not 5.x?

5.x is also interesting. Ubuntu LTE uses gcc-4.8 and latest Ubuntu uses 
gcc-4.9 so those two versions should ideally be tested too. Older 
versions than that are of little priority to me.

>> I'll do some new AVX and AVX2 tests.

FWIW I have yet to see anything calling for a change.

> Do you have pre-AVX machines to tune SSE2 and SSE4.1 interleaving on?
> I expect similar tradeoffs there, for Core 2 alikes (no HT) vs. early
> Core i7 (HT).

I could probably find some but again the test matrix quickly grows out 
of hands. Some day we should just build tests into ./configure (optional 
and along with an instruction to run on unloaded system and so on).

Actually we could just write some instructions instead, for using the 
already provided means: Run and then supply good values to 
./configure. It's not that inconvenient. Come to think of it, should end with printing a complete command line for 
./configure, ready for copy+paste. That I'll do right now.


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