linux-kernel - Re: [PATCH 2/5] perf script: extend db-export api to include callchains for samples

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Date:	Fri, 22 Apr 2016 21:41:56 -0700
From:	Chris Phlipot <cphlipot0@...il.com>
To:	Adrian Hunter <adrian.hunter@...el.com>, acme@...nel.org,
	mingo@...hat.com, peterz@...radead.org
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/5] perf script: extend db-export api to include
 callchains for samples



On 04/22/2016 12:56 AM, Adrian Hunter wrote:
> The call_paths table already has symbol_id which belongs uniquely to a DSO,
> so why do we need dso_id as well?
If the symbol_id is 0 because the IP could not be resolved to a symbol, 
this is not necessarily a valid assumption. Without a dso_id in the 
call_paths table, it is not possible to resolve the dso when symbol 
information is missing. the db_export api currently does not have enough 
information to match a DSO with an IP.

It is often useful to still have the call path associated with a DSO 
even if there is no symbol, which i why i recommend keeping the dso_id 
in the call_paths table.
> Why do you need a callback?  Seems like the only thing you need from
> thread-stack.c is the call path tree.  You could move that to its own .c/.h
> files and then process the call chain in db-export.c
My original intent was to reuse existing code with minimal changes and 
conform the existing design patterns they used. Thread-stack.c, for 
example, currently uses a callback to populate the call_return table, so 
I used a callback as well to populate the call_path table.

I am open to making this change if it is believed it will result in a 
cleaner implementation.
>
> Also a list of changes like the one above heavily implies you are not
> obeying the one patch == one change rule.  Please try to make patches that
> only do one thing and also run checkpatch.
While i can split this into a few smaller patches there is only really 
justification for applying all of them all together. If this is still 
preferred i can resubmit this in smaller parts.
>
> If you don't mind, I'll let you respond to my comments before I comment on
> any other patches.
>
Let me know if you have any additional comments.

Thanks,
Chris