Re: [dm-devel] [PATCH] backing-dev: use synchronize_rcu_expedited instead of synchronize_rcu

["Paul E. McKenney" <paulmck linux vnet ibm com>]

On Thu, Feb 02, 2012 at 10:59:04PM +0100, Peter Zijlstra wrote:
> On Thu, 2012-02-02 at 15:43 -0500, Mikulas Patocka wrote:
> > Do you have some measurable use case where the user is removing block 
> > devices so heavily that this causes a problem? 
> 
> Even one can be a problem, we're having people spend lots of time and
> effort to reduce machine wide jitter and interference. Adding it with
> such disregard isn't cool.
> 
> There's no reason a management cpu adding or removing block devices
> should perturb the high-freq trading or industrial laser control running
> on the other side of the machine.

Very true for real-time applications!

For the heavy trading apps, given Frederic's upcoming user-mode-idle work,
I can keep this stuff from perturbing the apps.  Still, batching would
be preferable.

							Thanx, Paul