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Re: [dm-devel] [PATCH 7/7] dm: optimize clone_rq() when track_peak_rq_based_ios is disabled



On Thu, Sep 12 2013 at  7:00pm -0400,
Mikulas Patocka <mpatocka redhat com> wrote:

> 
> 
> On Thu, 12 Sep 2013, Mike Snitzer wrote:
> 
> > Make use of static keys to eliminate the relevant branch in clone_rq()
> > when dm_mod's 'track_peak_rq_based_ios' paramter is set to 0 (disabled).
> > 
> > Even if 'track_peak_rq_based_ios' is set to 0 it will not take effect
> > until the next request-based table reload.  Once it is disabled the
> > 'peak_rq_based_ios' parameter will be reset to 0.
> 
> This patch changes it so that the value track_peak_rq_based_ios is sampled 
> only when reloading a table. I think it will be confusing to the user if 
> he changes the value, but the change doesn't take effect until something 
> reloads some table.

Well we need to be able to notice the change but I do not wish to do so
in a performance critical path (which clone_rq is).


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