Re: [PATCH RFC] nohz,blk-mq: do not create blk-mq workqueues on nohz dedicated CPUs

From: Jens Axboe
Date: Thu Apr 02 2015 - 21:15:48 EST


On 04/01/2015 10:12 AM, Rik van Riel wrote:
On 03/31/2015 11:43 AM, Jens Axboe wrote:

That'd be easy enough to do, that's how blk-mq handles offline CPUs as
well. The attached patch is completely untested, but will handle offline
or nohz CPUs in the same fashion - they will punt to hardware queue 0,
which is mapped to CPU0 (and others, depending on the queue vs CPU ratio).

I have done some sanity testing with your patch,
starting a KVM guest with vcpus and emulator threads
all pinned to nohz_full cpus.

The guest is still able to do disk IO, so things
appear to work...

Thanks for looking into this, Jens.

Tested-by: Rik van Riel <riel@xxxxxxxxxx>

Great thanks, I'll do some sanity testing here too and get it applied for 4.1.

--
Jens Axboe

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/