Hi Laszlo, On 06/14/2018 10:56 AM, Laszlo Ersek wrote: > Hi Eric, > > On 06/14/18 08:27, Auger Eric wrote: >> Hi Laszlo, >> >> On 06/13/2018 11:05 PM, Laszlo Ersek wrote: >>> On 06/13/18 10:48, Eric Auger wrote: >>> >>>> PATCH: merge of ECAM and VCPU extension >>>> - Laszlo reviewed the ECAM changes but I dropped his R-b >>>> due to the squash >>> >>> Was there any particular reason why the previous patch set (with only >>> the ECAM enlargement) couldn't be merged first? To be honest I'm not >>> super happy when my R-b is dropped for non-technical reasons; it seems >>> like wasted work for both of us. >>> >>> Obviously if there's a technical dependency or some other reason why >>> committing the ECAM enlargement in separation would be *wrong*, that's >>> different. Even in that case, wouldn't it be possible to keep the >>> initial virt-3.0 machtype addition as I reviewed it, and then add the >>> rest in an incremental patch? >> >> Sorry about that. My fear was about migration. We would have had 2 virt >> 3.0 machine models not supporting the same features. While bisecting >> migration we could have had the source using the high mem ECAM and the >> destination not supporting it. So I preferred to avoid this trouble by >> merging the 2 features in one patch. However I may have kept your R-b >> restricting its scope to the ECAM stuff. > > to my understanding, it is normal to *gradually* add new properties > during the development cycle, to the new machine type of the upcoming > QEMU release. To my understanding, it's not expected that migration work > between development snapshots built from git. What matters is that two > official releases, specifying the same machine type, enable the user to > migrate a guest between them (in forward direction). > > In every release, so many new features are introduced that it's > impossible to introduce the new machine type with all the compat knobs > added at once. Instead, the new machine type is introduced when the > first feature that requires a compat knob is added to git. All other > such features extend the compat knobs gradually, during the development > cycle. Until the new official release is made (which contains all the > compat knobs for all the new features), the new machine type simply > doesn't exist, as far as the public is concerned, so it cannot partake > in migration either. > > This is my understanding anyway.
Thank you for sharing your understanding. Maybe my concerns were superficial indeed. If Peter confirms there is no concern with bisection, I can easily repost the series splitting the virt machine model modifications in several patches, keeping your R-b ;-) Thanks Eric > > Thanks! > Laszlo >
