Re: [PATCH v6 16/20] IB/fmr_pool: Convert the cleanup thread into kthread worker API

[Doug Ledford <dledford@redhat.com>]

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On 04/14/2016 11:14 AM, Petr Mladek wrote:
> Kthreads are currently implemented as an infinite loop. Each
> has its own variant of checks for terminating, freezing,
> awakening. In many cases it is unclear to say in which state
> it is and sometimes it is done a wrong way.
> 
> The plan is to convert kthreads into kthread_worker or workqueues
> API. It allows to split the functionality into separate operations.
> It helps to make a better structure. Also it defines a clean state
> where no locks are taken, IRQs blocked, the kthread might sleep
> or even be safely migrated.
> 
> The kthread worker API is useful when we want to have a dedicated
> single thread for the work. It helps to make sure that it is
> available when needed. Also it allows a better control, e.g.
> define a scheduling priority.
> 
> This patch converts the frm_pool kthread into the kthread worker
> API because I am not sure how busy the thread is. It is well
> possible that it does not need a dedicated kthread and workqueues
> would be perfectly fine. Well, the conversion between kthread
> worker API and workqueues is pretty trivial.
> 
> The patch moves one iteration from the kthread into the work function.
> It preserves the check for a spurious queuing (wake up). Then it
> processes one request. Finally, it re-queues itself if more requests
> are pending.
> 
> Otherwise, wake_up_process() is replaced by queuing the work.
> 
> Important: The change is only compile tested. I did not find an easy
> way how to check it in a real life.

I had to do some digging myself to figure out how to move forward on
this patch.  The issue is that your conversion touches the fmr_pool code
as your target.  That code is slowly being phased out.  Right now, only
two drivers in the IB core support fmr: mthca and mlx4.  The generally
preferred method of mem management is fr instead of fmr.  The mlx4
driver support both fr and fmr, while the mthca driver is fmr only.  All
of the other drivers are fr only.  The only code that uses the fmr pools
are the upper layer iSER and SRP drivers.  So, if you have mthca
hardware, you can test fmr using either iSER or SRP clients.  If you
have mlx4 hardware, you can still test fmr by using the SRP client and
setting prefer_fr to false when you load the module.

Now that I know that, I can provide testing of this patch when the
overall patchset is ready to be submitted next.

-- 
Doug Ledford <dledford@redhat.com>
              GPG KeyID: 0E572FDD



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