Linux 3.15 Can Resume From Suspend 7~12x Faster

Early on in the Linux 3.15 merge window there were improvements to significantly speed-up suspend and resume for systems, but now there's another late merge of a patch that has the capability of speeding up the resume time from suspend by 7~12x for at least some laptop/desktop systems.

The work that was merged about two weeks ago for speeding up suspend and resume came down to enabling more asynchronous threads within the ACPI / power management code for different phases. By using more async threads, the time to both suspend and resume is dropped significantly.

The work that was merged on Friday night for the Linux 3.15 kernel primarily benefits the resume process. With work done by Intel, there's a much faster resume process due to async SCSI resume support. This work allows for disks and other devices to resume in parallel and yields performance benefits for real hardware.

Up to now the kernel resume process has been blocked by waiting for ATA devices to come online before resuming the boot process, but now with this merged patch the wakeup command is fired off and then returned immediately. This allows multiple ATA devices to be waked up concurrently. The rest of the kernel can also continue resuming while any commands sent to ATA/SCSI hardware is queued up until the device has notified the kernel that it's awake.

This resume benefit is written about at length on Intel's 01.org. Results shared by the developer show a 10.5x speedup for an Intel Core i7 3960X system resuming now in 1.1 seconds compared to 11.6 seconds previously, a 12x speed-up for an Intel Core i7 3770 system resuming in 0.45 seconds compared to 5.4 seconds in the past, and a 7.8x speedup for an Intel Core i7 4770S system resuming in 0.69 seconds compared to 5.4 seconds with the unpatched kernel.