linux-kernel - Re: [PATCH 3/3] cputime: Consolidate cputime adjustment code

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Date:	Mon, 26 Nov 2012 01:16:57 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Paul Gortmaker <paul.gortmaker@...driver.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH 3/3] cputime: Consolidate cputime adjustment code

2012/11/25 Paul Gortmaker <paul.gortmaker@...driver.com>:
>> --- a/include/linux/sched.h
>> +++ b/include/linux/sched.h
>> @@ -433,6 +433,11 @@ struct cpu_itimer {
>>       u32 incr_error;
>>  };
>>
>> +struct cputime {
>> +     cputime_t utime;
>> +     cputime_t stime;
>> +};
>> +
>
> Hi Frederic,
>
> This new struct cputime is a 2/3 subset of the three variable struct
> task_cputime we see right below.  Maybe this is a stupid question, but I
> was wondering why you didn't re-use task_cputime, and ignore the
> sum_exec_runtime field -- vs. introducing this very similar struct?

Not a stupid question, I need to add a comment on that. I avoided to
reuse struct task_cputime because sum_exec_runtime is unused and 8
wasted bytes in the middle of task_struct is very undesirable. As in
signal struct.

>
> Or maybe there is another way to consolidate the structs?  With the
> two being so similar, I wonder if it will be confusing when to use which
> one of the two.

I can add a comment that tells when to use which. Other than that I'm
short on ideas to consolidate both without creating a mess with long
dereferencing expressions like tsk->cputime.utime and so.
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