On Mon, Nov 25, 2019 at 12:48 PM Martin Wilck <mwilck@xxxxxxx> 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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