On Tue, Jan 14, 2014 at 09:43:25AM -0500, Tejun Heo wrote: > Hello, Gwendal. > > On Mon, Jan 13, 2014 at 04:36:52PM -0800, Gwendal Grignou wrote: > > Won't this patch defeat staggered spinup at resume? If you have a jbod > > with a smallish power supply, with a 12V rail designed for the steady > > state and 1 or 2 devices spinning up at once, you may be in trouble > > when all the disks will want to spinup in same second. > > Yeah, I think it would. We never fully solved the staggered spinup > problem and it probably is too late to invest into proper mechanism > for that. I think an easy workaround would be, say, have a kernel > param which limits the max number of concurrent async wakeups and set > the value to something reasonable - say, 2, which should give us most > of benefits of async wakeup in vast majority of cases while avoiding > blowing up PSUs on larger setups. Does my patch actually have any affect on staggered spinup? I see that when the HOST_CAP_SSS flag is detected it causes a PORT_CMD_SPIN_UP to be issued during each port's resume. But the port resume calls themselves appear to always be asynchronous, regardless of my patch's changes. (The ata_port devices all have their power.async_suspend flags set, so the dpm_resume call issues them all in parallel) So as far as I can tell I don't think I'm causing any harm. I do see how my patch might hinder future attempts at staggered resume handling, since it would effectively render the power.async_suspend flag useless. Would it be wise for ata_port_resume to check the ata_port's power.async_suspend flag and only use asynchronous ata_port_request_pm if it's enabled? > > Thanks. > > -- > tejun -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
