* Linus Torvalds <[EMAIL PROTECTED]> wrote:
> > I've run a few tests, just to get a few numbers of the overhead
> > involved. I used the last ~8,000 changesets from the BKCVS kernel
> > repository. With cold cache, a checkout from cold cache takes about
> > 250 seconds on my laptop. I don't have git numbers, but a mere copy
> > of the kernel tree needs 40 seconds.
>
> I will bet you that a git checkout is _faster_ than a kernel source
> tree copy. The time will be dominated by the IO costs (in particular
> the read costs), and the IO costs are lower thanks to compression. So
> I think that the cold-cache case will beat your 40 seconds by a clear
> margin. It generally compresses to half the size, so 20 seconds is not
> impossible (although seek costs would tend to stay constant, so I'd
> expect it to be somewhere in between the two).
i'd be surprised if it was twice as fast - cache-cold linear checkouts
are _seek_ limited, and it doesnt matter whether after a 1-2 msec
track-to-track disk seek the DMA engine spends another 30 microseconds
DMA-ing 60K uncompressed data instead of 30K compressed... (there are
other factors, but this is the main thing.)
Ingo
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