linux-kernel - Re: [PATCH v2 10/29] ktap: add string handling code(kernel/trace/ktap/kp

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Message-ID: <20140330171957.GF22728@two.firstfloor.org>
Date:	Sun, 30 Mar 2014 19:19:57 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Jovi Zhangwei <jovi.zhangwei@...il.com>
Cc:	Andi Kleen <andi@...stfloor.org>, Ingo Molnar <mingo@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH v2 10/29] ktap: add string handling
 code(kernel/trace/ktap/kp_[str|mempool].[c|h])

> See test/benchmark/cmp_table.sh, that script compare

Is that a realistic tracing scenario?

> table operation between ktap with stap, the result is very
> inspiring, ktap table operation overhead is quite lower than
> stap, especially when use constant string key.

Ok fair enough.

> 
> But I agree with you partly, because in some cases we don't
> want/need to interning all string, for example:
>     trace xxx:yyy {
>         var str = cast("char *", arg1)
>         print(str)
>     }
> 
> In above case, arg1 is a long kernel string, and no table insert,
> so definitely no need to interned, so we need to add
> KTAP_TRAWSTR to represent these values.

Please don't make it more complicated. If there's a good rationale
for interning it' ok to use always.

It would be better to find ways to simplify things.

-Andi
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