From: Ingo Molnar Date: Thu, 14 Apr 2005 07:04:22 GMT Subject: Re: Index/hash order Message-ID: <20050414070422.GA3226@elte.hu> In-Reply-To: * Linus Torvalds 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