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Re: Index/hash order

From
IMIngo Molnar <mingo@elte.hu>
Date
Apr 14, 2005, 07:04 UTC
Message-ID
<20050414070422.GA3226@elte.hu>
In-Reply-To
<Pine.LNX.4.58.0504131503180.4501@ppc970.osdl.org>
* Linus Torvalds <torvalds@osdl.org> wrote:
Show 13 quoted lines
> > 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
Previous: Florian WeimerNext: Ingo Molnar
Message 19 of 20 in “Re: Index/hash order”
  1. Ingo MolnarApr 13, 2005
  2. H. Peter AnvinApr 13, 2005
  3. Ingo MolnarApr 13, 2005
  4. Ingo MolnarApr 13, 2005
  5. Ingo MolnarApr 13, 2005
  6. Updated base64 patchesH. Peter Anvin, Apr 13, 2005
  7. Linus TorvaldsApr 13, 2005
  8. enforcing DB immutabilityIngo Molnar, Apr 20, 2005
  9. Ingo MolnarApr 20, 2005
  10. Ingo MolnarApr 20, 2005
  11. Chris WedgwoodApr 20, 2005
  12. Nick Craig-WoodApr 20, 2005
  13. WoutApr 27, 2005
  14. Linus TorvaldsApr 13, 2005
  15. Baruch EvenApr 13, 2005
  16. Florian WeimerApr 13, 2005
  17. Linus TorvaldsApr 13, 2005
  18. Florian WeimerApr 13, 2005
  19. Ingo MolnarApr 14, 2005
  20. cache-cold repository performanceIngo Molnar, Apr 14, 2005

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