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: <20130411210056.GS29861@linux.vnet.ibm.com>
Date:	Thu, 11 Apr 2013 14:00:56 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Randy Dunlap <rdunlap@...radead.org>
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 Thu, Apr 11, 2013 at 01:09:28PM -0700, Randy Dunlap wrote:
> 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>

I have added your Reviewed-by, thank you again!

							Thanx, Paul

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