On Wed, Mar 10, 2010 at 2:12 PM, Michael Tokarev <mjt@xxxxxxxxxx> wrote: > Neo Jia wrote: >> hi, >> >> I have to keep a 32-bit qmeu user space to work with some legacy >> library I have but still want to use 64-bit host Linux to explore >> 64-bit advantage. >> >> So I am wondering if I can use a 32-bit qemu + 64-bit kvm-kmod >> configuration. Will there be any limitation or drawback for this >> configuration? I already get one that we can't assign guest physical >> memory more than 2047 MB. > > I use 32bit kvm on 64bit kernel since the day one. Nothing of interest > since that, everything just works. Michael, I just came back to this thread because I am seeing that I can't run VISTA 64-bit inside 64/32 mode, which will crash with bugcheck 0x5D. Is this a known issue? > > Recently (this week) I come across a situation when something does not > work in 64/32 mode. Namely it is linux aio (see the other thread in > kvm@ a few days back) - but this is not due to kvm but due to other > kernel subsystem (in this case aio) which lacks proper compat handlers > in place. Could you tell me more about the AIO issue? Will this will slow down the guest if it does a lot I/O? Will setting up coalescing help? Thanks, Neo > > Generally I reported quite several issues in this config - here or there > there were issues, something did not work. Now the places where we've > issues are decreasing (hopefully anyway), at least I haven't seen issues > recently, except of this aio stuff. > > But strictly speaking, I don't see any good reason to run 32bit kvm on > 64 bit kernel either. Most distributions nowadays provide a set of > 64bit libraries for their 32bit versions so that limited support for > 64bit binaries are available. This is mostly enough for kvm - without > X and SDL support it works just fine (using vnc display). Historically > I've 32bit userspace, but most guests now are running with 64bit kvm - > either because the guests switched to 64bit kernel or because aio thing > or just because I looks like it is more efficient (less syscall/ioctl > 32=>64 translation and the like). kvm itself uses only very few memory > so here it almost makes no difference between 32 and 64 bits (in 64bit > pointers are larger and hence usually more memory is used). Yes, it is > difficult to provide everything needed for sdl, but for our tasks SDL > windows aren't really necessary, and for testing 32bit mode works just > fine too... > > /mjt > -- I would remember that if researchers were not ambitious probably today we haven't the technology we are using! -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
