In August 2010, Jens and Alan discussed about "Runtime PM and the block layer". http://marc.info/?t=128259108400001&r=1&w=2 And then Alan has given a detailed implementation guide: http://marc.info/?l=linux-scsi&m=133727953625963&w=2
To test: # ls -l /sys/block/sda /sys/devices/pci0000:00/0000:00:1f.2/ata1/host0/target0:0:0/0:0:0:0/block/sda # echo 10000 > /sys/devices/pci0000:00/0000:00:1f.2/ata1/host0/target0:0:0/0:0:0:0/power/autosuspend_delay_ms # echo auto > /sys/devices/pci0000:00/0000:00:1f.2/ata1/host0/target0:0:0/0:0:0:0/power/control Then you'll see sda is suspended after 10secs idle. [ 1767.680192] sd 2:0:0:0: [sda] Synchronizing SCSI cache [ 1767.680317] sd 2:0:0:0: [sda] Stopping disk And if you do some IO, it will resume immediately. [ 1791.052438] sd 2:0:0:0: [sda] Starting disk For test, I often set the autosuspend time to 1 second. If you are using a GUI, the 10 seconds delay may be too long that the disk can not enter runtime suspended state. Note that sd's runtime suspend callback will dump some kernel messages and the syslog daemon will write kernel message to /var/log/messages, making the disk instantly resume after suspended. So for test, the syslog daemon should better be temporarily stopped. A git repo for it, on top of libata/upstream, scsi/for-next and block/for-next: https://github.com/aaronlu/linux.git blockpm v8: - Set default autosuspend delay to -1 to avoid suspend till an updated value is set as suggested by Alan Stern; - Always check the dev field of the queue structure, as it is incorrect and meaningless to do any operation on devices that do not use block layer runtime PM as reminded by Alan Stern; - Update scsi bus level runtime PM callback to take care of scsi devices that use block layer runtime PM and that don't. v7: - Add kernel doc for block layer runtime PM API as suggested by Alan Stern; - Add back check for q->dev, as that serves as a flag if driver is using block layer runtime PM; - Do not auto suspend when last request is finished, as that's a hot path and auto suspend is not a trivial function. Instead, mark last busy in pre_suspend so that runtim PM core will retry suspend some time later to solve the 1st problem demostrated in v6, suggested by Alan Stern. - Move block layer runtime PM strtegy functions to where they are needed instead of in include/linux/blkdev.h as suggested by Alan Stern since clients of block layer do not need to know those functions. v6: Take over from Lin Ming. - Instead of put the device into autosuspend state in blk_post_runtime_suspend, do it when the last request is finished. This can also solve the problem illustrated below: thread A thread B |suspend timer expired | | ... ... |a new request comes in, | ... ... |blk_pm_add_request | ... ... |skip request_resume due to | ... ... |q->status is still RPM_ACTIVE | rpm_suspend | ... ... | scsi_runtime_suspend | ... ... | blk_pre_runtime_suspend | ... ... | return -EBUSY due to nr_pending | ... ... | rpm_suspend done | ... ... | | blk_pm_put_request, mark last busy But no more trigger point, and the device will stay at RPM_ACTIVE state. Run pm_runtime_autosuspend after the last request is finished solved this problem. - Requests which have the REQ_PM flag should not involve nr_pending counting, or we may lose the condition to resume the device: Suppose queue is active and nr_pending is 0. Then a REQ_PM request comes and nr_pending will be increased to 1, but since the request has REQ_PM flag, it will not cause resume. Before it is finished, a normal request comes in, and since nr_pending is 1 now, it will not trigger the resume of the device either. Bug. - Do not quiesce the device in scsi bus level runtime suspend callback. Since the only reason the device is to be runtime suspended is due to no more requests pending for it, quiesce it is pointless. - Remove scsi_autopm_* from sd_check_events as we are request driven. - Call blk_pm_runtime_init in scsi_sysfs_initialize_dev, so that we do not need to check queue's device in blk_pm_add/put_request. - Do not mark last busy and initiate an autosuspend for the device in blk_pm_runtime_init function. - Do not mark last busy and initiate an autosuspend for the device in block_post_runtime_resume, as when the request that triggered the resume finished, the blk_pm_put_request will mark last busy and initiate an autosuspend. v5: - rename scsi_execute_req to scsi_execute_req_flags and wrap scsi_execute_req around it. - add detail function descriptions in patch 2 log - define static helper functions to do runtime pm work on block layer and put the definitions inside a #ifdef block v4: - add CONFIG_PM_RUNTIME check - update queue runtime pm status after system resume - use pm_runtime_autosuspend instead of pm_request_autosuspend in scsi_runtime_idle - always count PM request v3: - remove block layer suspend/resume callbacks - add block layer runtime pm helper functions v2: - remove queue idle timer, use runtime pm core's auto suspend Lin Ming (4): block: add a flag to identify PM request block: add runtime pm helpers block: implement runtime pm strategy sd: change to auto suspend mode block/blk-core.c | 182 +++++++++++++++++++++++++++++++++++++++++++++ block/elevator.c | 26 +++++++ drivers/scsi/scsi_lib.c | 9 +-- drivers/scsi/scsi_pm.c | 79 +++++++++++++++++--- drivers/scsi/sd.c | 21 ++---- include/linux/blk_types.h | 2 + include/linux/blkdev.h | 27 +++++++ include/scsi/scsi_device.h | 16 +++- 8 files changed, 325 insertions(+), 37 deletions(-) -- 1.8.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
