linux-kernel - Re: linux-next: manual merge of the tip tree with the cputime tree

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Message-ID: <4EF0614A.9020402@parallels.com>
Date:	Tue, 20 Dec 2011 14:19:54 +0400
From:	Glauber Costa <glommer@...allels.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, <linux-next@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: linux-next: manual merge of the tip tree with the cputime tree

On 12/19/2011 06:08 PM, Peter Zijlstra wrote:
> On Mon, 2011-12-19 at 13:31 +0100, Martin Schwidefsky wrote:
>> Just one question: are you sure that you want the cpustat array
>> to be u64 instead of cputime64_t? The content of the cpustat array is defined
>> by the architecture semantics of cputime64_t, for CONFIG_VIRT_CPU_ACCOUNTING=y
>> this is not a jiffy counter. If the array is u64 we won't get the sparse
>> checking when reading from cpustat.
>
> So as Glauber said the reason was that we wanted to use simply
> operators, and IIRC he wanted to add a few fields that had to be u64.
>
> I'm not sure what the current plans are wrt adding more fields, but with
> your work cputime_t should again be a simple type and thus regular math
> operators should work again, right?
>
> Glauber, do you still need to add fields?

Due to the current state of discussions of cpu vs cpuacct, I think the 
final state of this is quite unclear. However, I think Martin's work is
a quite worthwhile piece for us to have. So last case we can add extra 
fields in a different array and tell them apart by the index, etc. It 
shouldn't be expensive at all.


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