Re: [Patch][RFC] Disabling per-tgid stats on task exit in taskstats

[Shailabh Nagar <nagar@watson.ibm.com>]

Jay Lan wrote:

>Shailabh Nagar wrote:
>  
>
>>Andrew Morton wrote:
>>
>>    
>>
>>>On Wed, 21 Jun 2006 12:11:13 -0700
>>>Jay Lan <jlan@engr.sgi.com> wrote:
>>>
>>> 
>>>
>>>      
>>>
>>>>Another observation that i considered bad news is that all
>>>>10 runs produced 1 to 5 recv() error with errno=105 (ENOBUF).
>>>>  
>>>>        
>>>>
>>>Well that's rather bad.  AFAICT most of the allocations in there are
>>>GFP_KERNEL, so why is this happening?
>>> 
>>>
>>>      
>>>
>>Need to trace the cause.
>>
>>    
>>
>>>Because the kernel is producing netlink messages faster than
>>>userspace can
>>>consume them, perhaps?
>>>      
>>>
>>Hmm...possible. A quick check would be to reduce the frequency of
>>exits and see.
>>
>>    
>>
>>>If so, the sender needs to block, which means we
>>>need to make reception of these stats a privileged operation?
>>> 
>>>
>>>      
>>>
>>Won't it suffice to make delivery of these stats best effort, with
>>userspace dealing with missing data,
>>    
>>
>
>How do you recover the missed data?
>  
>
Not recover as such but just let userspace know data was dropped so it 
can work around it.

>  
>
>>rather than risk delaying exits ? The cases where exits are so
>>frequent as in this program should be
>>    
>>
>
>This is very true. However, it was a 2p IA64 machine. I am too frightened to
>speak "512p"...
>  
>
True, but then you should presumably have more receivers or some other 
strategy to consume the output
faster ? Blocking is an even
worse idea if that many CPUs will be waiting around for stats data to be 
written out....


--Shailabh