On 2020/06/18 21:26, Simon Arlott wrote: > On 18/06/2020 09:36, Damien Le Moal wrote: >> On 2020/06/18 3:50, Simon Arlott wrote: >>> I need to use "reboot=p" on my desktop because one of the PCIe devices >>> does not appear after a warm boot. This results in a very cold boot >>> because the BIOS turns the PSU off and on. >>> >>> The scsi sd shutdown process does not send a stop command to disks >>> before the reboot happens (stop commands are only sent for a shutdown). >>> >>> The result is that all of my SSDs experience a sudden power loss on >>> every reboot, which is undesirable behaviour. These events are recorded >>> in the SMART attributes. >> >> Why is it undesirable for an SSD ? The sequence you are describing is not >> different from doing "shutdown -h now" and then pressing down the power button >> again immediately after power is cut... > > On a shutdown the kernel will send a stop command to the SSD. It does > not currently do this for a reboot so I observe the unexpected power > loss counters increasing. > >> Are you experiencing data loss or corruption ? If yes, since a clean reboot or >> shutdown issues a synchronize cache to all devices, a corruption would mean that >> your SSD is probably not correctly processing flush cache commands. > > No, I'm not experiencing any data loss or corruption that I'm aware of. > > We can argue whether or not any given SSD correctly processes commands > to flush the cache, but they are expecting to be stopped before power > is removed. > >>> Avoiding a stop of the disk on a reboot is appropriate for HDDs because >>> they're likely to continue to be powered (and should not be told to spin >>> down only to spin up again) but the default behaviour for SSDs should >>> be changed to stop them before the reboot. >> >> If your BIOS turns the PSU down and up, then the HDDs too will lose power... The >> difference will be that the disks will still be spinning from inertia on the >> power up, and so the HDD spin up processing will be faster than for a pure cold >> boot sequence. > > I haven't verified it, but the BIOS leaves the power off for several > seconds which should be long enough for the HDDs to spin down. > > I'm less concerned about those suddenly losing power but it would be > nice to have a stop command sent to them too. OK. So maybe the patch should be as simple as changing SYSTEM_RESTART state to SYSTEM_POWER_OFF if reboot=p is set, no ? Since that is consistent with the fact that reboot=p will cause power to go off, exactly the same as a regular shutdown, it seems cleaner and safer to use SYSTEM_POWER_OFF for the entire system, not just scsi disks. Thoughts ? -- Damien Le Moal Western Digital Research
