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Date: Wed, 26 Oct 2016 17:13:07 +0200 From: Arnd Bergmann <arnd@...db.de> To: Bart Van Assche <bart.vanassche@...disk.com> Cc: Jan Kara <jack@...e.cz>, Christoph Hellwig <hch@...radead.org>, Paolo Valente <paolo.valente@...aro.org>, Jens Axboe <axboe@...nel.dk>, Tejun Heo <tj@...nel.org>, linux-block@...r.kernel.org, linux-kernel@...r.kernel.org, ulf.hansson@...aro.org, linus.walleij@...aro.org, broonie@...nel.org, hare@...e.de, grant.likely@...retlab.ca, James.Bottomley@...senpartnership.com Subject: Re: [PATCH 00/14] introduce the BFQ-v0 I/O scheduler as an extra scheduler On Wednesday, October 26, 2016 8:05:11 AM CEST Bart Van Assche wrote: > On 10/26/2016 04:34 AM, Jan Kara wrote: > > On Wed 26-10-16 03:19:03, Christoph Hellwig wrote: > >> Just as last time: > >> > >> big NAK for introducing giant new infrastructure like a new I/O scheduler > >> for the legacy request structure. > >> > >> Please direct your engergy towards blk-mq instead. > > > > Christoph, we will probably talk about this next week but IMO rotating > > disks and SATA based SSDs are going to stay with us for another 15 years, > > likely more. For them blk-mq is no win, relatively complex IO scheduling > > like CFQ or BFQ does is a big win for them in some cases. So I think IO > > scheduling (and thus place for something like BFQ) is going to stay with us > > for quite a long time still. So are we going to add hooks in blk-mq to > > support full-blown IO scheduling at least for single queue devices? Or how > > else do we want to support that HW? > > Hello Jan, > > Having two versions (one for non-blk-mq, one for blk-mq) of every I/O > scheduler would be a maintenance nightmare. Has anyone already analyzed > whether it would be possible to come up with an API for I/O schedulers > that makes it possible to use the same I/O scheduler for both blk-mq and > the traditional block layer? 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). Arnd
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