Messages in this thread |  | | | Date | Thu, 12 Feb 2004 10:42:15 +0100 (CET) | | From | Giuliano Pochini <> | | Subject | Re: ext2/3 performance regression in 2.6 vs 2.4 for small interl |
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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.
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