-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On 3/24/15 9:20 AM, David Sterba wrote:
Hi,
currently the scsi-mq is set to Y, since 3.18-rc1 merge. The option enables a feature that makes advantage of enterprise-class storage. It's known not to perform well on slower devices [1] and lacks scheduler support.
That's overstating the problem a bit. It lacks scheduler support because as we encounter devices capable of much higher numbers of IOPS with essentially zero seek latency, the time we spend processing requests starts to take longer than the I/O itself. This isn't limited to enterprise storage. I can order a commodity SSD this morning that meets this description for about the same price as a regular hard drive (obviously with less capacity.)
We'll set the option to N in our stable kernels.
The lack of scheduler support can cause significant performance drop. Vojtech reports 10-50x slowdown on random read workloads, the disks seek all over the platters due to the missing io scheduler optimizations.
As most of our users are not likely to run on high-end storage devices or otherwise benefit from the scsi-mq feature, I believe it's safe to turn the scsi-mq option off. Once the io scheduler support is availabe we can enable it again.
The change will be done for all architectures and all kernel flavors (30 changes in total).
I disagree. This is a scenario that benefits some hardware and costs other hardware, which is effectively the same scenario that exists without SCSI_MQ_DEFAULT. The difference is that the single queue block layer is dying and the multiqueue block layer is evolving. The config option is the default and it can be changed at runtime. We're talking about Factory. If users with Vojtech's configuration (which is pretty esoteric - it's more than just having a few spinning disks) need to back off scsi-mq, they can do it by booting with scsi_mod.use_blk_mq=0. There is basic infrastructure in place to choose old block or blk-mq on a per-host basis but it hasn't been fleshed out yet. - -Jeff - -- Jeff Mahoney SUSE Labs -----BEGIN PGP SIGNATURE----- Version: GnuPG/MacGPG2 v2.0.19 (Darwin) iQIcBAEBAgAGBQJVEXiGAAoJEB57S2MheeWy9FsP/Rq/Ng/DFSzCJxypd8k5yUVH Tpc2oeC1fOVtdw8B8oX51DS4MYjy3aAD3LEFRtuHRc1tlbk0moxGR73upvphPVlj 7Wg/KUBO0hOLkLSUvPP+4xCeanSapK++DELw2982QiF5QT5qK9kqCr1EmYhrim1x P9ruDovb+xZu/O00Qcw1P9pu1SqsOI4+KcEWeU6zIqX7P77oiJJF988eq0Xid5N9 APS6wJKftsmSgEYMdGMfAtd+pm5bQaZWGSYd7ASXnSUgYLaPz6sL5TbP1t2X5Zrb 1mObokCFr/JB9RErew3P8G7lyMRtum0gnjsk9j4Elx6vsn3EpH9N080tyEXuQXDL Z+9Xis0DW1tu6ISl/QiCzPnyfHMaBWHuuDw7JKqzVDCedt1RBG84o9XghhoPPwWf rcE10cxJrlPal1XqO+bGTAEKiuEmjaPpjfzX0fDwRROgyL87KRsUUTT8gcwab9Jf Bi1sa6Zbc8a0nwL8OaUFNd0qU96se25xjF/qzDlBI9PHrNScUdxQJLQ1Cuswjs0R VnK5NPpTFTwiCqvpzIf4lxtEBr7Ba+8NuIfJtjaSZ/nD0M8CPxByu6NrYwhlLhmz 6RPcqC2CjMxtSXzJXcAoomV1gMwJvp7bYd6Jd80NCQPkNJMgKSyplnII0rb7FZ5/ Xl1YUaEae6Ts42/UZQSo =ukOh -----END PGP SIGNATURE----- -- To unsubscribe, e-mail: opensuse-kernel+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse-kernel+owner@opensuse.org