Messages in this thread |  | | Subject | Re: [PATCH] block: BFQ default for single queue devices | From | Bart Van Assche <> | Date | Fri, 5 Oct 2018 20:12:27 -0700 |
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On 10/5/18 2:16 AM, Jan Kara wrote: > On Thu 04-10-18 15:42:52, Bart Van Assche wrote: >> What I think is missing is measurement results for BFQ on a system with >> multiple CPU sockets and against a fast storage medium. Eliminating >> the host lock from the SCSI core yielded a significant performance >> improvement for such storage devices. Since the BFQ scheduler locks and >> unlocks bfqd->lock for every dispatch operation it is very likely that BFQ >> will slow down I/O for fast storage devices, even if their driver only >> creates a single hardware queue. > > Well, I'm not sure why that is missing. I don't think anyone proposed to > default to BFQ for such setup? Neither was anyone claiming that BFQ is > better in such situation... The proposal has been: Default to BFQ for slow > storage, leave it to deadline-mq otherwise.
Hi Jan,
How do you define slow storage? The proposal at the start of this thread was to make BFQ the default for all block devices that create a single hardware queue. That includes all SATA storage since scsi-mq only creates a single hardware queue when using the SATA protocol. The proposal to make BFQ the default for systems with a single hard disk probably makes sense but I am not sure that making BFQ the default for systems equipped with one or more (SATA) SSDs is also a good idea. Especially for multi-socket systems since BFQ reintroduces a queue-wide lock. As you know no queue-wide locking happens during I/O in the scsi-mq core nor in the blk-mq core.
Bart.
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