i have a server p4 2.4 (533) w/ 1gb ram and western digital WD1200JB-00DUA3 (8mb cache) hard drive.

under 2.4.x kernels my hdparm -Tt results are something around:

Timing buffer-cache reads: 470 MB/sec
Timing buffered disk reads: 47 MB/sec

after upgrading to 2.6.1 the performance fell drastically . the results are like:

Timing buffer-cache reads: 400 MB/sec
Timing buffered disk reads: 33 MB/sec

i have made sure that the tests are not affected by server load and memory cache etc. i also tried the latest hdparm package still got the same result.

my new kernel was compiled with based on the old configurations. DMA are indeed enabled and used. actually hdparm -Ii outputs the exactly same results under both kernels.

the weird thing is, i have another server p4 2.6 800fsb HT - SMP, 1gb ram and 3x80GB Maxtor hard drives. and the maxtor hd has no slow down at all under the new kernel. same benchmark results as in kernel 2.4.

any suggestions on this issue will be greatly appreciated. thanks.