On Thu, May 24, 2018 at 07:34:25AM +0200, Peter Krempa wrote: > On Wed, May 23, 2018 at 19:09:59 +0200, Andrea Bolognani wrote: > > On Wed, 2018-05-23 at 18:40 +0200, Peter Krempa wrote: > > > On Wed, May 23, 2018 at 18:18:02 +0200, Andrea Bolognani wrote: > > > > + /* QEMU expects the argument to be a number of left shifts: > > > > + * for example, if you wanted to limit the guest to 4 KiB pages, > > > > + * since 4096 == 1 << 12, you would need to add cap-hpt-mps=12 > > > > + * to the command line. > > > > > > So basically you need to pass the exponent of a power of 2 that yields > > > this number. The number of left shifts may be slightly confusing ... > > > > I guess it depends on the reader; the two definitions are > > equivalent anyway, so no harm in having both in the comment :) > > Using both are fine, but without mentioning that it is in fact a power of > two-only thing I was thinking that the interface is off by one or > something: > > 4096 == 1 << 12 == 2 << 11 > > > In general, I'd say it's not the most user-friendly interface on > > QEMU's side, but I believe it's dictated by hardware / emulator > > details, given how it ends up being used: see > > > > http://lists.nongnu.org/archive/html/qemu-devel/2018-04/msg02822.html > > > > To be fair, it would perhaps make sense to perform the conversion > > directly inside QEMU, in order to make it more convenient not only > > for libvirt but for for people driving it directly as well. > > If strictly only powers of two make sense for this knob then this gives > you input validation for free. On the other hand, specifying a big > number can overflow internally if it is ever used in the non-exponent > form. I think the format does not matter much, since libvirt's job is to > shield users from such weirdness. Yeah, the above is basically my reasoning for using the exponent, not the final page size. -- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson
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