Re: [RFC \ WISH] Add -o option to git-rev-list

[Linus Torvalds <torvalds@osdl.org>]

On Mon, 11 Dec 2006, Marco Costalba wrote:
> 
> $ time sh -c "git rev-list --header --boundary --parents --topo-order HEAD | cat > /dev/null"
> $ time sh -c "git rev-list --header --boundary --parents --topo-order HEAD > /tmp/tmp.txt; cat /tmp/tmp.txt > /dev/null"

Btw, for me the numbers aren't stable enough to be al lthat final, but 
doing it multiple times on the kernel archive I get:

	real    0m0.947s
	real    0m1.046s
	real    0m0.943s
	real    0m0.868s

for the pipe case, and

	real    0m0.953s
	real    0m1.056s
	real    0m1.060s
	real    0m0.968s

for the temp-file. IOW, no real difference. Just doing the "> /dev/null" 
directly is more consistent (no task-switching, SMP effects, or cache 
conflicts) at

	real    0m0.806s
	real    0m0.806s
	real    0m0.805s
	real    0m0.808s

but one recurrent theme is definitely true: the "cat" part is a noticeable 
overhead. But that in itself means that git-rev-list is just so efficient 
that even just basically copying its output is going to be measurable. 

Which is obviously a good thing, but it means that it's not very 
interesting in the big picture (ie I bet the real overheads are going to 
be elsewhere if you actually expect to draw anything on the screen).