[Pvfs2-developers] pvfs2-cp profile

[Scott Atchley]

On Jan 11, 2007, at 2:47 PM, Sam Lang wrote:

>>> So this 11 msec delay could be caused by writing to disk, but if  
>>> you don't have data sync enabled (which I don't think you do),  
>>> then 11 msec for 1 MB is about 90MB/s to write data to buffer  
>>> cache and return the write ack response.  We might be delayed  
>>> here by having to wait for flow buffers being free'd up from one  
>>> of the first 8 1MB messages.  Could you increase the  
>>> FlowBuffersPerFlow option in the fs.conf to 16 or 20 and see what  
>>> happens?
>>>
>>> -sam
>>
>> I will try this.
>>
>> I know that the default for FlowBuffersPerFlow is 8 per the  
>> webpage, but I count 10 per flow in the log. I also find that when  
>> using the -b flag, that it performs best with multiples of 10  
>> buffers.
>
> You're doing 10MB requests with 1MB flow buffers.  I think the 10  
> flows per request are from that, so the number of flow buffers is  
> still 8, it just has to reuse 2 of them.
>
> -b specifies the request size doesn't it?  Using multiples of 10  
> for that value improves performance?  I really have no idea, but  
> would have guessed that multiples of the flow buffer size (in your  
> case 1MB) would have been better.
>
> -sam

With FlowBuffersPerFlow set to 20, I am roughly the same gaps as  
before (~11 msec between last send completion and the recv completion  
and ~18 msec between transfers).

Scott