On 08/11/2019 17:47, Greg Kurz wrote: > On Fri, 8 Nov 2019 16:40:35 +0100 > Laurent Vivier <lviv...@redhat.com> wrote: > >> Commit 29cb4187497d sets by default the VSMT to smp_threads, >> but older kernels (< 4.13) don't support that. >> >> We can reasonably restore previous behavior with this kernel >> to allow to run QEMU as before. >> >> If VSMT is not supported, VSMT will be set to MAX(8, smp_threads) >> as it is done for previous machine types (< pseries-4.2) >> > > It is usually _bad_ to base the machine behavior on host capabilities.
This is already the case, statically: your patch guesses the kernel always support VSMT. So you can't start the machine (and thus can't migrate it to/from). > What happens if we migrate between an older kernel and a recent one ? I think migration is supported correctly only if parameters are explicitly set. So this is not our case. > I understand this is to fix tests/migration-test on older kernels. > Couldn't this be achieved with migration-test doing some introspection > and maybe pass vsmt=8 on the QEMU command line ? It could be a little bit complicated to instrospect this. We could also set by default vsmt=8 at the test level. Thanks, Laurent
