linux-kernel - Re: Performance Stats: Kernel patch

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Date:	Wed, 11 Apr 2007 21:22:46 +0200
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Maxim Uvarov <muvarov@...mvista.com>
CC:	linux-kernel@...r.kernel.org, davidsen@....com,
	randy.dunlap@...cle.com, Valdis.Kletnieks@...edu,
	jesper.juhl@...il.com
Subject: Re: Performance Stats: Kernel patch

Maxim Uvarov a écrit :
> Eric Dumazet wrote:
> 
>  >Please check kernel/sys.c:k_getrusage() to see how getrusage() has to 
> sum *lot* of individual fields to get precise process numbers (even 
> counting stats for dead threads)
> 
> 
> 
> Thanks for helping me and for this link. But it is not enough clear for 
> me what do you mean at this time.  Inside of patch I am using 2 default 
> counters
> task_struct->nivcsw and task_struct->nvcsw. And also one new syscall 
> counter. And there is only one way to increment this counter, it is from 
> entry.S.
> 
> If you are speaking about locks,  in my point of view, they are not 
> needed in this code. Because increment syscall counter is atomic for X86 
> (just one assembly instruction) and in case with PPC (3 instructions) 
> there 1) nothing wrong will not happen in any case 2) only own thread 
> can increase it's syscall counter. So here should be not any race 
> conditions.

I was not speaking about locks.

> 
> I've tested this patch on x86,x86_64,and ppc_32. And I should work now 
> with ppc_64 (I didn't check).
> And  also updated description.
> 
> Best regards,
> Maxim Uvarov.
> 
> 
> ------------------------------------------------------------------------
> 
> Patch adds Process Performance Statistics.
> It make available to the user the following 
> thread performance statistics:
>    * Involuntary Context Switches (task_struct->nivcsw)
>    * Voluntary Context Switches (task_struct->nvcsw)
>    * Number of system calls (added new counter 
>      thread_info->sysc_cnt)
> 
> Statistics information is available from
> /proc/PID/status
>    
> This data is useful for detecting hyperactivity 
> patterns between processes.
> 

What I meant is : You falsely speak of 'PROCESS performance statistics'.

Your implementation only cares about threads, not processes.
There is a slight difference, that getrusage() can do.

So if you do "cat /proc/PID/status", you'll get counters not for the PROCESS, 
only the main thread of the process.

If you want an analogy, imagine a "ps aux" that doesnt show the cpu time of 
all threads of a process, but only the cpu time of the main thread. Quite 
meaningless isnt it ?

So either :

1) You change all your description to mention 'thread' instead of 'process'.

2) You change your implementation to match your claim.

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