R515/H700 high iowait

Dennis Jacobfeuerborn dennisml at conversis.de
Wed Jul 18 08:52:09 CDT 2012


On 07/18/2012 03:37 PM, Mark Nelson wrote:
> On 7/18/12 7:26 AM, G.Bakalarski at icm.edu.pl wrote:
>>
>>> This is with XFS and barriers were left enabled.  We also tested having
>>> fio write directly to the device.
>>
>> Hi Mark,
>>
>> Did you enable any virtualization settings ???
>> Does your Ubuntu runs on bare metal hardware without
>> any xen, citrix or whatever???
>>
>> Did you changes anything in BIOS setting eg.
>> IOMMU on (DMA virtualisation) ? What is your
>> C states setting? Is BIOS optimized for Performance
>> (CPU seting)?
>>
>> Have you monitored IO behaviour with e.g. iostat -xzk 2 ???
>> What was a size of queue length? Did it change during tests?
>> Have you tested IO with another tools like e.g. iozone or others ??
>>
>> Bests,
>>
>> GB
>>
>>
> 
> Hi GB,
> 
> Looks like virtualization technology is on in the bios, but DMA 
> virtualization is off.  OS is running on bare metal.
> 
> C1E is on, which should probably be disabled.  CPU Power and Performance 
> Management is set to Maximum Performance.
> 
> While I did not run iostat specifically, I did run collectl with the 
> disk subsystem on during some of the tests.
> 
> Here's an example when things are bad (ie multiple writers):
> 
>> #                   <---------reads---------><---------writes---------><--------averages--------> Pct
>> #Time     Name       KBytes Merged  IOs Size  KBytes Merged  IOs Size  RWSize  QLen  Wait SvcTim Util
>> 11:18:40 sdb              0      0    0    0   24964      0  196  127     127   142   725      5   99
>> 11:18:41 sdb              0      0    0    0   22272      0  174  128     128   142   925      5   99
>> 11:18:42 sdb              0      0    0    0   30464      0  238  128     128   145   716      4   99
> 
> And when things are good (256MB requests, DirectIO, one writer):
> 
>> #                   <---------reads---------><---------writes---------><--------averages--------> Pct
>> #Time     Name       KBytes Merged  IOs Size  KBytes Merged  IOs Size  RWSize  QLen  Wait SvcTim Util
>> 11:29:32 sdb              0      0    0    0  737920      0 5765  128     128   119    20      0   87
>> 11:29:33 sdb              0      0    0    0  798464      0 6238  128     128   126    20      0   95
>> 11:29:34 sdb              0      0    0    0  798976      0 6242  128     128   126    20      0   94
>

May I ask which tool you use to get this output? This particular way to
display these numbers looks quite nice.

Regards,
  Dennis



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