Messages in this thread | | | Subject | Re: [PATCH RFC] block, bfq: set default slice_idle to zero for non-rotational devices | From | Paolo Valente <> | Date | Fri, 2 Nov 2018 21:18:26 +0300 |
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> Il giorno 1 nov 2018, alle ore 22:06, Holger Hoffstätte <holger@applied-asynchrony.com> ha scritto: > > On 11/01/18 18:43, Konstantin Khlebnikov wrote: >> With default 8ms idle slice BFQ is up to 10 times slower than CFQ >> for massive random read workloads for common SATA SSD. >> For now zero idle slice gives better out of box experience. >> CFQ employs this since commit 41c0126b3f22 ("block: Make CFQ default >> to IOPS mode on SSDs") > > Well, that's interesting because 3 years ago I made the same suggestion > and was told that BFQ's heuristics automagically make it not idle when > rotational=0.
Yep, that automagic is probably 50% of the good of BFQ.
If one just sets slice_idle=0, then throughput is always maximum with random I/O; but there is no control on I/O any longer.
At any rate, Konstantin, if you have some use case where BFQ fails, I'll be very glad to analyze it, and hopefully improve BFQ. Just one request: use at least a 4.19.
Thanks, Paolo
> Did you actually benchmark this? I just tried and don't > get a noticeable performance difference with slice_idle=0 compared to > deadline. > > Discussion link: > https://groups.google.com/forum/#!msg/bfq-iosched/iRMw2n3kYLY/6l9cIm3TBgAJ > > curious.. > > Holger
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