linux-kernel - Re: [PATCH V2 2/7] mm/gup: add gup trace points

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Date:	Thu, 3 Dec 2015 14:06:14 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	"Shi, Yang" <yang.shi@...aro.org>
Cc:	Dave Hansen <dave.hansen@...el.com>, akpm@...ux-foundation.org,
	mingo@...hat.com, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linaro-kernel@...ts.linaro.org
Subject: Re: [PATCH V2 2/7] mm/gup: add gup trace points

On Thu, 03 Dec 2015 10:36:18 -0800
"Shi, Yang" <yang.shi@...aro.org> wrote:

> > called directly that calls these functions internally and the tracepoint
> > can trap the return value.  
> 
> This will incur more changes in other subsystems (futex, kvm, etc), I'm 
> not sure if it is worth making such changes to get return value.

No, it wouldn't require any changes outside of this.

-long __get_user_pages(..)
+static long __get_user_pages_internal(..)
{
  [..]
}
+
+long __get_user_pages(..)
+{
+	long ret;
+	ret = __get_user_pages_internal(..);
+	trace_get_user_pages(.., ret)
+}

> 
> > I can probably make function_graph tracer give return values, although
> > it will give a return value for void functions as well. And it may give
> > long long returns for int returns that may have bogus data in the
> > higher bits.  
> 
> If the return value requirement is not limited to gup, the approach 
> sounds more reasonable.
>

Others have asked about it. Maybe I should do it.

-- Steve

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