Swsusp approaches readiness

The new laptop has the same little "suspend" symbol on the same key, but it doesn't work. In the modern, ACPI world, it is the operating system which is responsible for suspending and resuming the system. This change is, somehow, presented as progress. The version of Windows shipped with the laptop is able to perform this operation, of course. Strangely, Sony does not support Linux to the same level. Your editor, it seems, was doomed to head off to the Kernel Summit and OLS with a non-suspending laptop.

Then came the announcement that software suspend for 2.4, v1.0, was available. LWN has covered the swsusp patch before, but swsusp has long been in the "almost works" category. For a long time, it appeared that not much was being done in that area. More recently, the swsusp effort has picked up steam (as more kernel hackers get new laptops, perhaps). Thus, the 1.0 release.

The swsusp tarball yielded a series of patches; the user has to decide which ones to apply depending on what other patches are of interest. For example, if the target (2.4.21) kernel has the ACPI patches in it (pretty much mandatory for many laptops), a separate swsusp "option" patch must be applied as well. The swsusp "Applying" file covers the necessary patches (and required order) reasonably well - for somebody who is comfortable messing with highly patched kernels.

The patch also comes with a "hibernate" script which is used to actually kick off a software suspend operation. This (lengthy) script tries to get everything into shape for a graceful suspend; in many ways, it behaves like a partial shutdown. Certain processes are killed off, as many modules as possible are unloaded, etc. On resume it restores the clock, reconfigures network interfaces, and, perhaps, engages in some complicated gymnastics in an effort to get X and the video hardware back in sync.

The bottom line is: it works. On your editor's laptop, an invocation of hibernate saves state and takes the system to a power-off state in 16 seconds. Returning to a full X display takes a little longer: 34 seconds, after the BIOS finishes its power-on ablutions. To say the least, this is a nice functionality to have in a laptop, especially when one is attempting to cover a conference.

The one bit of remaining difficulty is the laptop's Radeon video hardware, which refuses to come back into any sort of reasonable, useful state. There is, evidently, a patch for XFree86 which makes this problem go away. But your editor, who has no trouble with patching a kernel to a pulp, shies away from patching and installing XFree86. It was far simpler to tell X to run in the unaccelerated, dumb frame buffer mode, which works just fine.

For those who are interested in 2.4 software suspend, the first swsusp 1.1 release candidate was announced on August 5. There's a number of useful changes in this version, but the largest is probably the ability to save system state to swapfiles (previous versions only worked with swap partitions). Software suspend support in 2.6 is in more of a state of flux; the power management changes have still not been merged, and work is being done to make the swsusp support cleaner, more flexible, and more robust. 2.6 should eventually have a solid swsusp implementation, though it may still be stabilizing when 2.6.0 comes out. It is unclear whether swsusp will ever be merged into the 2.4 kernel; it is a somewhat invasive patch to apply to a stable series.