Re: [PATCH RFC V2 3/3] scsi_mq: enable runtime PM

Alan Stern
2018-07-18T14:12:37Z

On Wed, 18 Jul 2018, Johannes Thumshirn wrote:

> On Wed, Jul 18, 2018 at 08:06:10PM +0800, Ming Lei wrote:
> > IMO the problem isn't related with slow or quick device, it is related with
> > the system, especially when it cares about power consumption, such as
> > mobile phone, or laptop or servers with lots of disks attached. And we know
> > it is often to see some fast disks shipped in laptop, such as NVMe, or other
> > SSD.
>
> Yes but you're only taking locally attached devices into account.
> This is very likely harmful on sd devices attached to a
> SRP/FC/iSCSI/SAS Target in a SAN environment. These can be really fast
> and people investing this money are likely to not like additional
> performance penalties.

As one extra reminder... People who care about extreme performance can
perfectly well disable CONFIG_PM in their kernels. That should remove
any overhead due to runtime PM.

Alan Stern