On Thu, 14 Aug 2008, Nicolas Pitre wrote:

quoted text
>

> > so most of it is in inflate,

>

> Which, again, would be eliminated entirely by pack v4.

I seriously doubt that.
Nico, it's really easy to say "I wave my magic wand and nothing remains".
It's hard to actually _do_.
> One optimization with pack v4 was to have delta chunks aligned on tree

quoted text
> records, and because tree objects are no longer compressed, parsing a

> tree object could be done by simply walking the delta chain directly.  

Even if you do that, please take a look at the performance characteristics

of modern CPU's.
Here's a hint: the cost of a cache miss is generally about a hundred times

the cost of just about anything else. 
So to make a convincing argument, you'd have to show that the actual

memory access patterns are also much better.
No, zlib isn't perfect, and nope, inflate_fast() is no "memcpy()". And

yes, I'm sure a pure memcpy would be much faster. But I seriously suspect

that a lot of the cost is literally in bringing in the source data to the

CPU. Because we just mmap() the whole pack-file, the first access to the

data is going to see the cost of the cache misses.
			Linus

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