On Tue, 24 Jul 2007, Huang, Ying wrote: > >From: Alan Stern [mailto:stern@xxxxxxxxxxxxxxxxxxx] > >It can't. Indeed, in the absence of a freezer, user threads will need > >devices (more accurately, will submit I/O requests for devices) that > >have to be kept quiescent or low-power. Drivers will need to delay > >those requests until the devices are returned to full operation. > > > >That's exactly what I've been saying all along: Drivers will need to > >be changed to delay I/O requests, if there is no freezer. > > If it is a too big work to implement "delaying I/O requests" for every > driver, is it possible to implement it as follow: > > 1. It is triggered to suspend to RAM/DISK. > 2. Replace the driver related syscall entries (such as sys_read, > sys_write, sys_ioctl, etc) in sys_call_table with special wrapper > entries provided by "suspend to RAM/DISK" subsystem, which will delay > I/O requests if appropriate. > 3. When devices are quiesced, they are put into "low power" state and > system is put into suspend state; or the image is written to disk > (through snapshot/uswsusp or kexeced kernel). > 4. After resuming from RAM/DISK, devices are put into "normal" state and > the syscall entries replaced in step 2 are restored. Ha! I made exactly this same suggestion (URL lost in the mists of time), except that I proposed changing the syscall entries for every system call, not just the driver-related ones. Nobody seemed to think it would work very well. It leaves a few loose ends. For example, suppose a user thread is already in the middle of a system call and is about to start doing some I/O (maybe it's waiting for a timer to expire). In the end, this doesn't seem to be very different from freezing all user threads. Alan Stern _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
