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SubjectRe: ext2/3 performance regression in 2.6 vs 2.4 for small interleaved writes
Andrew Morton wrote:

>So you'll see that instead of a single full-bandwidth
>write, we do two half-bandwidth writes. If it weren't for disk writeback
>caching, it would be as much as 4x slower.
Write caching does indeed make a big difference. Here is a test run on a
drive with and without write caching (hdparm -W 0/1). The test was done
on 2.6.2 with ext3 and shows the write speed in MB/s:

Write Cache 1 Stream 2 Streams
Enabled 21.54 3.66
Disabled 18.11 0.46

The two stream case is almost 10x slower without write caching.
I don't think this explains the difference between 2.4 and 2.6 unless
one of them changes the write cache mode of the drive.


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