linux-kernel - Re: [PATCH documentation 2/2] kthread: Document ways of reducing OS jitter due to per-CPU kthreads

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Message-ID: <51671878.9050800@infradead.org>
Date:	Thu, 11 Apr 2013 13:09:28 -0700
From:	Randy Dunlap <rdunlap@...radead.org>
To:	paulmck@...ux.vnet.ibm.com
CC:	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, josh@...htriplett.org,
	niv@...ibm.com, tglx@...utronix.de, peterz@...radead.org,
	rostedt@...dmis.org, Valdis.Kletnieks@...edu, dhowells@...hat.com,
	edumazet@...gle.com, darren@...art.com, fweisbec@...il.com,
	sbw@....edu, Borislav Petkov <bp@...en8.de>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Kevin Hilman <khilman@...aro.org>,
	Christoph Lameter <cl@...ux.com>
Subject: Re: [PATCH documentation 2/2] kthread: Document ways of reducing
 OS jitter due to per-CPU kthreads

On 04/11/13 11:40, Paul E. McKenney wrote:
> On Thu, Apr 11, 2013 at 10:18:26AM -0700, Randy Dunlap wrote:
>> On 04/11/2013 09:05 AM, Paul E. McKenney wrote:
>>> From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
>>>
>>> The Linux kernel uses a number of per-CPU kthreads, any of which might
>>> contribute to OS jitter at any time.  The usual approach to normal
>>> kthreads, namely to affinity them to a "housekeeping" CPU, does not
>>
>> ugh.               to affine them
> 
> How about s/affinity/bind/ instead?

Yes, that's good.

>>> work with these kthreads because they cannot operate correctly if moved
>>> to some other CPU.  This commit therefore lists ways of controlling OS
>>> jitter from the Linux kernel's per-CPU kthreads.
>>>
>>> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
>>> Cc: Frederic Weisbecker <fweisbec@...il.com>
>>> Cc: Steven Rostedt <rostedt@...dmis.org>
>>> Cc: Borislav Petkov <bp@...en8.de>
>>> Cc: Arjan van de Ven <arjan@...ux.intel.com>
>>> Cc: Kevin Hilman <khilman@...aro.org>
>>> Cc: Christoph Lameter <cl@...ux.com>
>>> ---
>>>  Documentation/kernel-per-CPU-kthreads.txt | 159 ++++++++++++++++++++++++++++++
>>>  1 file changed, 159 insertions(+)
>>>  create mode 100644 Documentation/kernel-per-CPU-kthreads.txt
>>>
>>> diff --git a/Documentation/kernel-per-CPU-kthreads.txt b/Documentation/kernel-per-CPU-kthreads.txt
>>> new file mode 100644
>>> index 0000000..495dacf
>>> --- /dev/null
>>> +++ b/Documentation/kernel-per-CPU-kthreads.txt
>>> @@ -0,0 +1,159 @@
>>> +REDUCING OS JITTER DUE TO PER-CPU KTHREADS
>>> +
>>> +
>>> +Name: irq/%d-%s
>>> +Purpose: Handle threaded interrupts.
>>> +To reduce corresponding OS jitter, do the following:
>>> +1.	Use irq affinity to force the irq threads to execute on
>>> +	some other CPU.
>>
>> It would be very nice to explain here how that is done.
> 
> Documentation/IRQ-affinity.txt
> 
> I added a pointer to this near the beginning.
> 

Good.

> Thank you for your review and comments!  Given my rationale above,
> are you still comfortable with my applying your Reviewed-by?

Sure.  Thanks.

>> Reviewed-by: Randy Dunlap <rdunlap@...radead.org>


-- 
~Randy
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