Re: Git and GCC

From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Dec 7, 2007, 17:23 UTC
Message-ID: <alpine.LFD.0.9999.0712070919590.7274@woody.linux-foundation.org>
In-Reply-To: <20071207.045329.204650714.davem@davemloft.net>

On Fri, 7 Dec 2007, David Miller wrote:

Show 7 quoted lines

> 
> Also I could end up being performance limited by SHA, it's not very
> well tuned on Sparc.  It's been on my TODO list to code up the crypto
> unit support for Niagara-2 in the kernel, then work with Herbert Xu on
> the userland interfaces to take advantage of that in things like
> libssl.  Even a better C/asm version would probably improve GIT
> performance a bit.

I doubt yu can use the hardware support. Kernel-only hw support is inherently broken for any sane user-space usage, the setup costs are just way way too high. To be useful, crypto engines need to support direct user space access (ie a regular instruction, with all state being held in normal registers that get saved/restored by the kernel).

> Is SHA a significant portion of the compute during these repacks?
> I should run oprofile...

SHA1 is almost totally insignificant on x86. It hardly shows up. But we have a good optimized version there.

zlib tends to be a lot more noticeable (especially the uncompression: it may be faster than compression, but it's done _so_ much more that it totally dominates).

			Linus