linux-kernel - Re: [PATCH 03/27] cputime: Allow dynamic switch between tick/virtual based cputime accounting

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Date:	Mon, 7 Jan 2013 16:47:31 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Paul Gortmaker <paul.gortmaker@...driver.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Alessio Igor Bogani <abogani@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Chris Metcalf <cmetcalf@...era.com>,
	Christoph Lameter <cl@...ux.com>,
	Geoff Levand <geoff@...radead.org>,
	Gilad Ben Yossef <gilad@...yossef.com>,
	Hakan Akkan <hakanakkan@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 03/27] cputime: Allow dynamic switch between tick/virtual
 based cputime accounting

Hey Paul,

2013/1/4 Paul Gortmaker <paul.gortmaker@...driver.com>:
> On 12-12-29 11:42 AM, Frederic Weisbecker wrote:
>> Allow to dynamically switch between tick and virtual based cputime accounting.
>> This way we can provide a kind of "on-demand" virtual based cputime
>> accounting. In this mode, the kernel will rely on the user hooks
>> subsystem to dynamically hook on kernel boundaries.
>>
>> This is in preparation for beeing able to stop the timer tick further
>> idle. Doing so will depend on CONFIG_VIRT_CPU_ACCOUNTING which makes
>
> s/beeing/being/  -- also I know what you mean, but it may not be
> 100% clear to everyone -- perhaps "...for being able to stop the
> timer tick in more places than just the idle state."

Thanks! Fixed for the next version!

[...]
>> +static inline bool vtime_accounting(void) { return false; }
>
> It wasn't 100% obvious what vtime_accounting() was doing until I
> saw its definition below.  I wonder if it should be something like
> vtime_accounting_on() or vtime_accounting_enabled() instead?

Agreed, I've renamed into vtime_accounting_enabled().

>
>>  #endif
>>
>>  #ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
>> diff --git a/init/Kconfig b/init/Kconfig
>> index dad2b88..307bc35 100644
>> --- a/init/Kconfig
>> +++ b/init/Kconfig
>> @@ -342,6 +342,7 @@ config VIRT_CPU_ACCOUNTING
>>       bool "Deterministic task and CPU time accounting"
>>       depends on HAVE_VIRT_CPU_ACCOUNTING || HAVE_CONTEXT_TRACKING
>>       select VIRT_CPU_ACCOUNTING_GEN if !HAVE_VIRT_CPU_ACCOUNTING
>> +     select VIRT_CPU_ACCOUNTING_NATIVE if HAVE_VIRT_CPU_ACCOUNTING
>>       help
>>         Select this option to enable more accurate task and CPU time
>>         accounting.  This is done by reading a CPU counter on each
>> @@ -366,11 +367,16 @@ endchoice
>>
>>  config VIRT_CPU_ACCOUNTING_GEN
>>       select CONTEXT_TRACKING
>> +     depends on VIRT_CPU_ACCOUNTING && HAVE_CONTEXT_TRACKING
>
> Should the 2nd half of this depends been already here, i.e. introduced
> with the prev. patch that created VIRT_CPU_ACCOUNTING_GEN?

Yeah, Li Zhong suggested that I turn *_GEN and *_NATIVE options into
distinct choices for the user. So I moved that part to the previous
patch.

Thanks!
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