On 10/26/2016 09:29 AM, Christoph Hellwig wrote:
On Wed, Oct 26, 2016 at 05:13:07PM +0200, Arnd Bergmann wrote:
The question to ask first is whether to actually have pluggable
schedulers on blk-mq at all, or just have one that is meant to
do the right thing in every case (and possibly can be bypassed
completely).
That would be my preference. Have a BFQ-variant for blk-mq as an
option (default to off unless opted in by the driver or user), and
not other scheduler for blk-mq. Don't bother with bfq for non
blk-mq. It's not like there is any advantage in the legacy-request
device even for slow devices, except for the option of having I/O
scheduling.
It's the only right way forward. blk-mq might not offer any substantial
advantages to rotating storage, but with scheduling, it won't offer a
downside either. And it'll take us towards the real goal, which is to
have just one IO path. Adding a new scheduler for the legacy IO path
makes no sense. Adding one for blk-mq and phasing out the old path is
what we need to do.
--
Jens Axboe
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