On 10/20/2015 05:03 PM, Frederic Weisbecker wrote:
On Tue, Oct 20, 2015 at 04:36:06PM -0400, Chris Metcalf wrote:
While the current fallback to 1-second tick is still required for
a number of kernel accounting tasks (e.g. vruntime, load balancing
data, and load accounting), it's useful to be able to disable it
for testing purposes. Paul McKenney observed that if we provide
a mode where the 1Hz fallback timer is removed, this will provide
an environment where new code that relies on that tick will get
punished, and we won't forgive such assumptions silently.
This option also allows easy testing of nohz_full and task-isolation
modes to determine what functionality needs to be implemented,
and what possibly-spurious timer interrupts are scheduled when
the basic 1Hz tick has been turned off.
Signed-off-by: Chris Metcalf <cmetcalf@xxxxxxxxxx>
There have been proposals to disable/tune the 1 Hz tick via debugfs which
I Nacked because once you give such an opportunity to the users, they
will use that hack and never fix the real underlying issue.
For the same reasons, I'm sorry but I have to Nack this proposal as well.
If this is for development or testing purpose, scheduler_max_tick_deferment() is
easily commented out.
Fair enough and certainly your prerogative, so don't hesitate to
say "no" to the following argument. :-)
I would tend to differentiate a debugfs proposal from a boot flag
proposal: a boot flag is a more hardcore thing to change, and it's
not like application developers will come along and explain that
you have to boot with different flags to run their app - whereas
if they can just sneak in a modification to a debugfs setting that's
much easier for the app to tweak.
So perhaps a boot flag is an acceptable compromise between
"nothing" and a debugfs tweak? It certainly does make it easier
to hack on the task-isolation code, and likely other things where
people are trying out fixes to subsystems where they are attempting
to remove the reliance on the tick.
--
Chris Metcalf, EZChip Semiconductor
http://www.ezchip.com
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