Re: Linux Software RAID 5 Performance Optimizations: 2.6.19.1: (211MB/s read & 195MB/s write)

[Bill Davidsen <davidsen@tmr.com>]

Justin Piszcz wrote:
> # echo 3 > /proc/sys/vm/drop_caches
> # dd if=/dev/md3 of=/dev/null bs=1M count=10240
> 10240+0 records in
> 10240+0 records out
> 10737418240 bytes (11 GB) copied, 399.352 seconds, 26.9 MB/s
> # for i in sde sdg sdi sdk; do   echo 192 > 
> /sys/block/"$i"/queue/max_sectors_kb;   echo "Set 
> /sys/block/"$i"/queue/max_sectors_kb to 192kb"; done
> Set /sys/block/sde/queue/max_sectors_kb to 192kb
> Set /sys/block/sdg/queue/max_sectors_kb to 192kb
> Set /sys/block/sdi/queue/max_sectors_kb to 192kb
> Set /sys/block/sdk/queue/max_sectors_kb to 192kb
> # echo 3 > /proc/sys/vm/drop_caches
> # dd if=/dev/md3 of=/dev/null bs=1M count=10240 
> 10240+0 records in
> 10240+0 records out
> 10737418240 bytes (11 GB) copied, 398.069 seconds, 27.0 MB/s
>
> Awful performance with your numbers/drop_caches settings.. !
>
> What were your tests designed to show?
>   
To start, I expect then to show change in write, not read... and IIRC (I 
didn't look it up) drop_caches just flushes the caches so you start with 
known memory contents, none.
>
> Justin.
>
> On Fri, 12 Jan 2007, Justin Piszcz wrote:
>
>   
>> On Fri, 12 Jan 2007, Al Boldi wrote:
>>
>>     
>>> Justin Piszcz wrote:
>>>       
>>>> RAID 5 TWEAKED: 1:06.41 elapsed @ 60% CPU
>>>>
>>>> This should be 1:14 not 1:06(was with a similarly sized file but not the
>>>> same) the 1:14 is the same file as used with the other benchmarks.  and to
>>>> get that I used 256mb read-ahead and 16384 stripe size ++ 128
>>>> max_sectors_kb (same size as my sw raid5 chunk size)
>>>>         
>>> max_sectors_kb is probably your key. On my system I get twice the read 
>>> performance by just reducing max_sectors_kb from default 512 to 192.
>>>
>>> Can you do a fresh reboot to shell and then:
>>> $ cat /sys/block/hda/queue/*
>>> $ cat /proc/meminfo
>>> $ echo 3 > /proc/sys/vm/drop_caches
>>> $ dd if=/dev/hda of=/dev/null bs=1M count=10240
>>> $ echo 192 > /sys/block/hda/queue/max_sectors_kb
>>> $ echo 3 > /proc/sys/vm/drop_caches
>>> $ dd if=/dev/hda of=/dev/null bs=1M count=10240
>>>
>>>       

-- 
bill davidsen <davidsen@tmr.com>
  CTO TMR Associates, Inc
  Doing interesting things with small computers since 1979