[dm-devel] multipath - unable to use multiple active paths at once, and deprecated example in docs

[Drew Hastings]

On Mon, Nov 25, 2019 at 12:48 PM Martin Wilck <mwilck at suse.de> wrote:

>
> I think you are seeing this FIXME:
>
> https://elixir.bootlin.com/linux/v4.19.79/source/drivers/md/dm-mpath.c#L612
>
> For your testing, perhaps you just remove that if(!pgpath) condition.
>
> Regards,
> Martin
>

That's correct, thanks. It works as expected after removing that condition.

With some limited testing using fio, I don't see any obvious negative
impacts of allowing choose_pgpath to run each bio mapping. I also don't see
any significant increase in CPU usage or IO latency during benchmarking.

The FIXME comment acknowledges that this sort of defeats the balancing
function of multipath, so I'm assuming this was removed for a good reason.
Does anyone know why this was done? In my particular use case, I benefit
from balancing the paths for throughput, so it's useful to me.

Thanks!
- Drew
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