Avi Kivity wrote:
Anthony Liguori wrote:
Avi Kivity wrote:
Anthony Liguori wrote:
Another place "hook" is updating a slot's dirty bitmap. Right now,
with my patchset we don't have live migration or the VGA RAM
optimization. There's nothing about the VGA RAM optimization that
wouldn't work for QEMU. I'm not sure that it really is an
optimization in the context of TCG, but I certainly don't think
it's any worse. The only thing you really need is to query the KVM
dirty bitmap when it comes time to enable start over querying the
VGA dirty bits.
I don't understand this. The VGA optimization really is qemu's, the
kvm modifications only cater to the different way of getting the
dirty bits.
Right. I'm just not sure that it's going to be as much of an
optimization for TCG as it is for KVM.
When qemu is loaded certainly this is lost in the noise. But when
idling (and as a bonus, the screen doesn't change much), tcg and kvm
will benefit equally.
Right now, in QEMU, code looks like this:
for (i = 0; i < addr; i += TARGET_PAGE_SIZE) {
if (cpu_p_m_g_dirty(i, DIRTY_FLAG)) {
cpu_p_m_r_dirty(i, i + TARGET_PAGE_SIZE, DIRTY_FLAG);
// do something with dirty memory
}
All we need to do is add another cpu_physical_memory_sync_dirty(i, i
+ REGION_SIZE, DIRTY_FLAG); that would go at the start of this. For
QEMU, this is a nop since dirty bits are updated as soon as they are
reset. For KVM, this would update the entire set of dirty bits for
the given memory region.
You mean merge the kvm bitmap into the qemu bitmap? That's what it
does now, no?
We also need something to enable dirty tracking for a particular
region. We already have something for migration, we could perhaps
extend that API (cpu_p_m_s_dirty_tracking).
I don't think qemu would benefit much from per-region tracking, but
maybe I'm wrong.
QEMU doesn't do per region tracking but instead, uses flags to simulate
regions. At any rate, the suggestion for an API to enable dirty
tracking was really for KVMs benefit. It's a nop for QEMU.
Regards,
Anthony Liguori
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