These patches attempt to help disks that are spun down stay that way, until they are actually accessed. The first patch deals with disks in SLEEP mode ( hdparm -Y ). SLEEP mode is a lower power mode than STANDBY. Linux has had support for it for a long time, however, if you try to make use of it, you quickly find that the disk wakes up for no apparent reason. This is because in SLEEP mode, the disk electronics are powered off so that it can not respond to any command. Waking the disk up requires a SATA link reset. There are a number of commands that are regularly issued to a disk in standby that the disk treats as a NOOP, but in SLEEP mode, these commands trigger the SATA link reset to wake up the drive in order to send the command to the drive. This patch deals with this by completing the commands in libata rather than waking the drive. The third patch is about how system suspend/resume effects disks in standby. Archive disks that are very rarely accessed may spend most of their lives in standby, but every time the system is suspended and resumed, they spin up, only to be spun back down again. This wastes power and puts wear and tear on the drive that is not neccesary. ATA drives have a feature called Power Up In Standby that allows the drive to not automatically spin up when the system is resumed. There are two different types of PuiS: one that acts like regular standby, in that any command that requires access to the disk will automatically spin the disk up, and another that requires an explicit SET FEATURES command to bring it out of PuiS mode. The kernel used to let the former type remain in standby after system resume, but recent changes have changed that behavior. This patch attempts to allow both types to remain spun down after system resume, until they are actually accessed. It currently has two paths for doing so. The one that is currently active is to simply set the ATA_DFLAG_SLEEPING flag and leave the drive in standby mode. This flag causes a later attempt to access the drive to trigger a round of EH that resets the SATA link, revalidates the drive, and if needed, issude the SET FEATURES command to bring it out of PuiS mode. The alternative path ( currently #if 0'd out ) actually issues the SLEEP command to put the drive into SLEEP mode. This can possibly save a little more power than leaving it in standby mode, but the transition from standby to sleep may not be legal according ot the ATA standards. This therefore, may upset some drives ( though it works fine with mine ). It therefore is not suitable as a default. I am thinking of adding a sysfs knob to control the PuiS behavior with 3 states: 0: wake the disk anyhow ( current behavior ) 1: leave the disk in standby mode 2: put the disk to SLEEP I think the worst thing that can happen with the third option is that some disks might error and you will get some clutter in your syslog while EH happens. People can try this option and fall back to #1 if they encounter issues. Otherwise, they can enjoy the added power savings. Finally, the second patch addresses an issue where the third patch's clearing of the SET_ACTIVE flag was countermanded. This was because the flag is set every time the EH starts during system resume. In my case, putting the drive to SLEEP caused a second round of EH to happen as the SATA PHY is shut down during SLEEP. That turned on the SET_ACTIVE flag again, causing a VERIFY command to try to start the drive, which failed because the drive requires the SET FEATURES command to come out of PuiS mode. Phillip Susi (3): libata: avoid waking disk for several commands libata: only wake a drive once on system resume libata: don't start PuiS disks on resume drivers/ata/libata-core.c | 61 ++++++++++++++++++++++++++++++++++----- drivers/ata/libata-eh.c | 20 +++++++++---- drivers/ata/libata.h | 3 +- include/linux/libata.h | 1 + 4 files changed, 70 insertions(+), 15 deletions(-) -- 2.30.2
