Re: [PATCH] mingw: use OpenSSL's SHA-1 routines

> On Thu, Feb 09, 2017 at 11:27:49PM +0100, Johannes Schindelin wrote:
> 
> > From: Jeff Hostetler <jeffhost@microsoft.com>
> > 
> > Use OpenSSL's SHA-1 routines rather than builtin block-sha1 routines.
> > This improves performance on SHA1 operations on Intel processors.
> > 
> > OpenSSL 1.0.2 has made considerable performance improvements and
> > support the Intel hardware acceleration features.  See:
> > https://software.intel.com/en-us/articles/improving-openssl-performance
> > https://software.intel.com/en-us/articles/intel-sha-extensions
> > 
> > To test this I added/staged a single file in a gigantic repository
> > having a 450MB index file.  The code in read-cache.c verifies the
> > header SHA as it reads the index and computes a new header SHA as it
> > writes out the new index.  Therefore, in this test the SHA code must
> > process 900MB of data.  Testing was done on an Intel I7-4770 CPU @
> > 3.40GHz (Intel64, Family 6, Model 60) CPU.
> 
> I think this is only half the story. A heavy-sha1 workload is faster,
> which is good. But one of the original reasons to prefer blk-sha1 (at
> least on Linux) is that resolving libcrypto.so symbols takes a
> non-trivial amount of time. I just timed it again, and it seems to be
> consistently 1ms slower to run "git rev-parse --git-dir" on my machine
> (from the top-level of a repo).
> 
> 1ms is mostly irrelevant, but it adds up on scripted workloads that
> start a lot of git processes.