Re: Queries on using PERF tool

[Namhyung Kim <namhyung@kernel.org>]

Hi Shahina,

2012-11-29 (목), 13:45 +0530, Shahina Rabbani:
> Hi Namhyung Kim ,
> 
> 
> First of all Thanks for your mail.
> I have some more doubts. Please help me.
> 
> 
> Q1: when we are working with more than one CPU, there will be a shared
> L2 cache for all the CPUs and each CPU will have its own L1-cache
>        If i want to monitor a event and i am using L1-cahce and
> L2-caches from CPU1 and the same time if CPU2 is also trying to
> monotora particular event and using L2-  
>        cache. Then how the perf tool handles this situation.

On a recent kernel and Intel cpus, it supports offcore and/or uncore
events for that purpose AFAIK.  Please check your cpu manuals.

> 
> 
> Q2.  Can you please list what are the architechtures it is supporting
> at present.
> 
> 
> Q3.  Consider the case of Distributed systems, where the processors
> are connected through the network and say i am trying to transmit data
> over the TCP/IP stack. Is it 
>         possible to monitor the data send at our end and data received
> from the other end using the perf tool??

The perf tools work with pipe so that we might use nc/netcat for this.
Only tested on a local machine:

<on terminal 1>
$ nc -l localhost 8282 | perf report -i -

<on terminal 2>
$ perf record -o - sleep 1 | nc localhost 8282


> 
> 
> Q4. when using perf record. Say i have got the data in perf.data file.
> Say i am using this file to get some information and assume that
> system crashes and the perf.data file is 
>       in inconsistent state. when u reboot the system after the crash,
> is it posssible to get the perf.data file safely.???

I doubt you can use the file safely.  There's no guarantee when system
crashed.

Thanks,
Namhyung

> 
> 
> Q5. Say i am counting some samples depending on the clock. and assume
> that i change the clock in between., Then the perf tool will be able
> to understand the situation and count the samples depending on the old
> and ne changed clocks or do we need to provide this information to
> perf tool.?? how to handle this situation??