From: Linus Torvalds <torvalds@linux-foundation.org>
To: Jeff King <peff@peff.net>
Cc: Johannes Schindelin <johannes.schindelin@gmx.de>,
Git Mailing List <git@vger.kernel.org>,
Jeff Hostetler <jeffhost@microsoft.com>,
Junio C Hamano <gitster@pobox.com>
Subject: Re: [PATCH] mingw: use OpenSSL's SHA-1 routines
Date: Fri, 24 Feb 2017 16:44:09 -0800 [thread overview]
Message-ID: <CA+55aFxY2CMJxdDs-LGChJFxHmhjnifEoi-aDV3AmDu8goM+rg@mail.gmail.com> (raw)
In-Reply-To: <20170210050237.gajicliueuvk6s5d@sigill.intra.peff.net>
On Thu, Feb 9, 2017 at 9:02 PM, Jeff King <peff@peff.net> wrote:
>
> 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).
Yes. It's also a horrible plain to profile those things.
Avoiding openssl was a great thing, because it avoided a lot of crazy overhead.
I suspect that most of the openssl win comes from using the actual SHA
instructions on modern CPU's. Because last I looked, the hand-coded
assembly simply wasn't that much faster.
We could easily have some x86-specific library that just does "use SHA
instructions if you have them, use blk-sha1 otherwise".
Of course, if we end up using the collision checking SHA libraries
this is all moot anyway.
Linus
prev parent reply other threads:[~2017-02-25 0:45 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-02-09 22:27 [PATCH] mingw: use OpenSSL's SHA-1 routines Johannes Schindelin
2017-02-09 23:41 ` Junio C Hamano
2017-02-11 8:01 ` Johannes Sixt
2017-02-11 18:51 ` Junio C Hamano
2017-02-13 17:16 ` Johannes Schindelin
2017-02-16 18:12 ` Johannes Sixt
2017-02-10 5:02 ` Jeff King
2017-02-10 15:49 ` Johannes Schindelin
2017-02-10 16:04 ` Jeff King
2017-02-13 17:46 ` Johannes Sixt
2017-02-13 19:42 ` Junio C Hamano
2017-02-13 21:07 ` Johannes Sixt
2017-02-13 22:38 ` Johannes Schindelin
2017-02-14 6:14 ` Johannes Sixt
2017-02-24 21:54 ` Junio C Hamano
2017-03-02 6:07 ` Johannes Sixt
2017-03-02 17:07 ` Junio C Hamano
2017-02-25 0:44 ` Linus Torvalds [this message]
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