Messages in this thread | | | Date | Thu, 12 Feb 2004 15:59:41 +0100 | From | Andrea Arcangeli <> | Subject | Re: ext2/3 performance regression in 2.6 vs 2.4 for small interl |
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On Thu, Feb 12, 2004 at 10:42:15AM +0100, Giuliano Pochini wrote: > > On 12-Feb-2004 Andrea Arcangeli wrote: > > > the main difference is that 2.4 isn't in function of time, it's in > > function of requests, no matter how long it takes to write a request, > > so it's potentially optimizing slow devices when you don't care about > > latency (deadline can be tuned for each dev via > > /sys/block/*/queue/iosched/). > > IMHO it's the opposite. Transfer speed * seek time of some > slow devices is lower than fast devices. For example: > > Hard disk raw speed= 40MB/s seek time = 8ms > MO/ZIP raw speed= 3MB/s seek time = 25ms > > One seek of HD costs about 320KB, while on a slow drive it's > only 75KB. 2.4 has a terrible latency on slow devices, and it > has very small advantage in terms of speed. On CDs and DVDs > the cost of a seek is much higher, but since the data is > usually accessed sequentially you have the high latency > penalty with no appreciable speed gain in this case too.
I was thinking at old slow harddisks (5M/sec), and I don't think all data on cds is always accessed sequentially, you only need two tasks reading two files. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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