-----BEGIN PGP SIGNED MESSAGE-----
On 03/31/2015, 03:30 PM, Jiri Slaby wrote:
On 03/24/2015, 03:45 PM, Jeff Mahoney wrote:
On 3/24/15 9:20 AM, David Sterba wrote:
> 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  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
> The lack of scheduler support can cause
> 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
> 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
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
The config option is the default and it can be
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.
Ping: this is a month now. I will revert the change in master and
merge to stable if there are no objections?
It has been a week now and it remained disabled. So
what is the
result of this thread, please?
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v2
-----END PGP SIGNATURE-----
To unsubscribe, e-mail: opensuse-kernel+unsubscribe(a)opensuse.org
To contact the owner, e-mail: opensuse-kernel+owner(a)opensuse.org