On Thursday, July 9, 2020 9:04:30 PM CEST Dan Williams wrote: > On Thu, Jul 9, 2020 at 7:57 AM Rafael J. Wysocki <rjw@xxxxxxxxxxxxx> wrote: > > > > On Tuesday, July 7, 2020 3:59:32 AM CEST Dan Williams wrote: > > > The runtime firmware activation capability of Intel NVDIMM devices > > > requires memory transactions to be disabled for 100s of microseconds. > > > This timeout is large enough to cause in-flight DMA to fail and other > > > application detectable timeouts. Arrange for firmware activation to be > > > executed while the system is "quiesced", all processes and device-DMA > > > frozen. > > > > > > It is already required that invoking device ->freeze() callbacks is > > > sufficient to cease DMA. A device that continues memory writes outside > > > of user-direction violates expectations of the PM core to be to > > > establish a coherent hibernation image. > > > > > > That said, RDMA devices are an example of a device that access memory > > > outside of user process direction. RDMA drivers also typically assume > > > the system they are operating in will never be hibernated. A solution > > > for RDMA collisions with firmware activation is outside the scope of > > > this change and may need to rely on being able to survive the platform > > > imposed memory controller quiesce period. > > > > Thanks for following my suggestion to use the hibernation infrastructure > > rather than the suspend one, but I think it would be better to go a bit > > further with that. > > > > Namely, after thinking about this a bit more I have come to the conclusion > > that what is needed is an ability to execute a function, inside of the > > kernel, in a "quiet" environment in which memory updates are unlikely. > > > > While the hibernation infrastructure as is can be used for that, kind of, IMO > > it would be cleaner to introduce a helper for that, like in the (untested) > > patch below, so if the "quiet execution environment" is needed, whoever > > needs it may simply pass a function to hibernate_quiet_exec() and provide > > whatever user-space I/F is suitable on top of that. > > > > Please let me know what you think. > > This looks good to me in concept. > > Would you expect that I trigger this from libnvdimm sysfs, or any > future users of this functionality to trigger it through their own > subsystem specific mechanisms? Yes, I would. > I have a place for it in libvdimm and could specify the activation > method directly as "suspend" vs "live" activation. Sounds good to me. Cheers!
