Date: Thu, 15 Dec 2016 22:34:51 -0600 From: Justin Hibbits <chmeeedalf@gmail.com> To: =?ISO-8859-1?Q?Roger_Pau_Monn=E9?= <roger.pau@citrix.com> Cc: FreeBSD Arch <freebsd-arch@freebsd.org> Subject: Re: Order of device suspend/resume Message-ID: <CDAA6577-C325-4691-9317-8CB0CE30959D@gmail.com> In-Reply-To: <7469755.xT5lfhErkd@ralph.baldwin.cx> References: <20161215114033.r33nt3fqhnfi7hqw@dhcp-3-221.uk.xensource.com> <7469755.xT5lfhErkd@ralph.baldwin.cx>
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On Dec 15, 2016, at 3:38 PM, John Baldwin wrote: > On Thursday, December 15, 2016 11:40:33 AM Roger Pau Monné wrote: >> Hello, >> >> I'm currently dealing with a bug in the Xen suspend/resume >> sequence, and I've >> found that lacking a way to order device priority during suspend/ >> resume is >> proving quite harmful for Xen (and maybe other systems too). The >> current >> suspend/resume code simply scans the root bus, and suspends/resumes >> every device >> based on the order they are attached to their parents. The problem >> here is that >> there's no way to tell that some devices should be resumed before >> others, for >> example the event timers/time counters/uarts should definitely be >> resume before >> other devices, but that's seems to happens mostly out of chance. >> >> Currently most time related devices are attached directly to the >> nexus, which >> means they will get resumed first, but for example the uart is >> currently >> attached to the pci bus IIRC, which means it gets resumed quite >> late. On Xen >> systems, this is even worse. The Xen PV bus (that contains all Xen- >> related >> devices) is attached the last one (because it tends to pick up >> unused memory >> regions for it's own usage) and this bus also contains the PV >> timecounter which >> should be resumed _before_ other devices, or else timecounting will >> be >> completely screwed and things can get stuck in indefinitely long >> loops (due to >> the fact that the timecounter is implemented based on the uptime of >> the host, >> and that changes from host-to-host). >> >> In order to solve this I could add a hack to the Xen resume process >> (which is >> already different from the ACPI one), but this looks gross. I could >> also attach >> the Xen PV timer to the nexus directly (as it was done before), but >> I also >> prefer to keep all Xen-related devices in the same bus for >> coherency. Last >> option would be to add some kind of suspend/resume priorities to >> the devices, >> and do more than one suspend/resume pass. This is more complex and >> requires more >> changes, so I would like to know if it would be helpful for other >> systems, or if >> someone has already attempted to do it. > > I think Justin Hibbits had some patches to make use of the boot-time > new-bus > passes for suspend and resume which I think would help with this. > You suspend > things in the reverse order of boot and resume operates in the same > order as > boot. > > -- > John Baldwin John is right. I have a (somewhat abandoned due to time and focus) branch, https://svnweb.freebsd.org/base/projects/pmac_pmu/ which has the necessary code working mostly on PowerPC. The diff can be found at https://reviews.freebsd.org/D203 too. - Justinhome | help
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