Messages in this thread | | | Date | Sat, 2 May 2015 21:52:30 -0400 | From | Tejun Heo <> | Subject | Re: [PATCH v6] block: loop: avoiding too many pending per work I/O |
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Hello,
On Sat, May 02, 2015 at 10:56:20PM +0800, Ming Lei wrote: > > Maybe just cap max_active to NR_OF_LOOP_DEVS * 16 or sth? But idk, > > It might not work because there are nested loop devices like fedora live CD, and > in theory the max_active should have been set as loop's queue depth * > nr_loop, otherwise there may be possibility of hanging. > > So this patch is introduced.
If loop devices can be stacked, regardless of what you do with nr_active, it may deadlock. There needs to be a rescuer per each nesting level (or just one per device). This means that the current code is broken.
> > how many concurrent workers are we talking about and why are we > > capping per-queue concurrency from worker pool side instead of command > > tag side? > > I think there should be performance advantage to make queue depth a bit more > because it can help to make queue pipeline as full. Also queue depth often > means how many requests the hardware can queue, and it is a bit different > with per-queue concurrency.
I'm not really following. Can you please elaborate?
Thanks.
-- tejun
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