REGRESSION in 2.6.13-rc1: Massive slowdown with Adaptec SCSI

From: Neil Brown
Date: Mon Jul 04 2005 - 20:09:35 EST



Hi,
I have a server with a:
SCSI storage controller: Adaptec AHA-3960D / AIC-7899A U160/m (rev 01)
Subsystem: Adaptec AHA-3960D U160/m

connected to 14
Vendor: MAXTOR Model: ATLAS15K_36SCA Rev: DTA0

7 on each channel.

On 2.6.12 a simple 'dd' write test gives 70 Meg/second:

cage # time dd of=/dev/null if=/dev/sdl bs=1024k count=100
100+0 records in
100+0 records out
104857600 bytes transferred in 1.555210 seconds (67423431 bytes/sec)

real 0m1.557s
user 0m0.001s
sys 0m0.770s


On 2.6.13-rc1 the same test takes just short on 1 minute and reports
slightly less than 2 M/Second.

cage # time dd of=/dev/null if=/dev/sdl bs=1024k count=100
100+0 records in
100+0 records out
104857600 bytes transferred in 54.576592 seconds (1921293 bytes/sec)

real 0m54.578s
user 0m0.000s
sys 0m0.360s

I'm happy to try patches or perform other tests.

NeilBrown
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