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

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Message-ID: <5660BDC2.5060400@linaro.org>
Date:	Thu, 03 Dec 2015 14:10:10 -0800
From:	"Shi, Yang" <yang.shi@...aro.org>
To:	Steven Rostedt <rostedt@...dmis.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 12/3/2015 11:06 AM, Steven Rostedt wrote:
> 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)
> +}

Thanks for this. I just checked the fast version, it looks it just has 
single return path, so this should be just needed by slow version.

>
>>
>>> 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.

If you are going to add return value in common trace code, I won't do 
the gup specific one in V3.

Thanks,
Yang

>
> -- Steve
>

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