On Fri, Feb 21, 2020 at 09:56:54AM +0000, Durrant, Paul wrote: > > -----Original Message----- > > From: Roger Pau Monné <roger....@citrix.com> > > Sent: 21 February 2020 09:22 > > To: Durrant, Paul <pdurr...@amazon.co.uk> > > Cc: Agarwal, Anchal <ancha...@amazon.com>; Valentin, Eduardo > > <edu...@amazon.com>; len.br...@intel.com; pet...@infradead.org; > > b...@kernel.crashing.org; x...@kernel.org; linux...@kvack.org; > > pa...@ucw.cz; h...@zytor.com; t...@linutronix.de; sstabell...@kernel.org; > > fllin...@amaozn.com; Kamata, Munehisa <kama...@amazon.com>; > > mi...@redhat.com; xen-devel@lists.xenproject.org; Singh, Balbir > > <sbl...@amazon.com>; ax...@kernel.dk; konrad.w...@oracle.com; > > b...@alien8.de; boris.ostrov...@oracle.com; jgr...@suse.com; > > net...@vger.kernel.org; linux...@vger.kernel.org; r...@rjwysocki.net; > > linux-ker...@vger.kernel.org; vkuzn...@redhat.com; da...@davemloft.net; > > Woodhouse, David <d...@amazon.co.uk> > > Subject: Re: [Xen-devel] [RFC PATCH v3 06/12] xen-blkfront: add callbacks > > for PM suspend and hibernation > > > > On Thu, Feb 20, 2020 at 05:01:52PM +0000, Durrant, Paul wrote: > > > > > Hopefully what I said above illustrates why it may not be 100% > > common. > > > > > > > > Yes, that's fine. I don't expect it to be 100% common (as I guess > > > > that the hooks will have different prototypes), but I expect > > > > that routines can be shared, and that the approach taken can be the > > > > same. > > > > > > > > For example one necessary difference will be that xenbus initiated > > > > suspend won't close the PV connection, in case suspension fails. On PM > > > > suspend you seem to always close the connection beforehand, so you > > > > will always have to re-negotiate on resume even if suspension failed. > > > > > > > > What I'm mostly worried about is the different approach to ring > > > > draining. Ie: either xenbus is changed to freeze the queues and drain > > > > the shared rings, or PM uses the already existing logic of not > > > > flushing the rings an re-issuing in-flight requests on resume. > > > > > > > > > > Yes, that's needs consideration. I don’t think the same semantic can be > > suitable for both. E.g. in a xen-suspend we need to freeze with as little > > processing as possible to avoid dirtying RAM late in the migration cycle, > > and we know that in-flight data can wait. But in a transition to S4 we > > need to make sure that at least all the in-flight blkif requests get > > completed, since they probably contain bits of the guest's memory image > > and that's not going to get saved any other way. > > > > Thanks, that makes sense and something along this lines should be > > added to the commit message IMO. > > > > Wondering about S4, shouldn't we expect the queues to already be > > empty? As any subsystem that wanted to store something to disk should > > make sure requests have been successfully completed before > > suspending. > > What about writing the suspend image itself? Normal filesystem I/O > will have been flushed of course, but whatever vestigial kernel > actually writes out the hibernation file may well expect a final > D0->D3 on the storage device to cause a flush.
Hm, I have no idea really. I think whatever writes to the disk before suspend should actually make sure requests have completed, but what you suggest might also be a possibility. Can you figure out whether there are requests on the ring or in the queue before suspending? > Again, I don't know the specifics for Linux (and Windows actually > uses an incarnation of the crash kernel to do the job, which brings > with it a whole other set of complexity as far as PV drivers go). That seems extremely complex, I'm sure there's a reason for it :). Thanks, Roger. _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
