Re: SCSI mid layer and high IOPS capable devices

[Bart Van Assche <bvanassche@acm.org>]

On 12/13/12 19:03, scameron@beardog.cce.hp.com wrote:
> What are your system specs?

A quad core Intel i5-2400 @ 3.10 GHz.

> 	taskset -c "$cpu" dd if="$device" of=/dev/null bs=4k iflag=direct

Please use fio instead of dd for any serious performance measurements. 
dd doesn't even guarantee that it's buffers are page aligned.

> I don't have "disable-frequency-scaling" on rhel6, but I think if I send
> SIGUSR1 to all the cpuspeed processes, this does the same thing.

Depends on which scaling governor and minimum frequency has been 
configured. This is what I am using:

#!/bin/bash
for d in /sys/devices/system/cpu/cpu*/cpufreq
do
   if [ -e "$d/scaling_governor" ]; then
     echo "userspace" >"$d/scaling_governor"
     echo "$(<$d/cpuinfo_max_freq)" >"$d/scaling_min_freq"
   fi
done

And the test I ran is:

fio --bs=4096 --ioengine=libaio --rw=randread --buffered=0 --thread    \
     --numjobs=${cpucount} --iodepth=16 --iodepth_batch=8               \
     --iodepth_batch_complete=8                                         \
     --loops=$((2**31)) --runtime=60 --group_reporting --size=${size}   \
     --gtod_reduce=1 --name=${dev} --filename=${dev} --invalidate=1

Bart.