On 9/23/24 14:46, Sean Christopherson wrote:
On Mon, Sep 23, 2024, Denis Plotnikov wrote:
On 9/22/24 11:04, Sean Christopherson wrote:
On Tue, Sep 17, 2024, Denis Plotnikov wrote:
It's helpful to know whether some other host activity affects a virtual
machine to estimate virtual machine quality of sevice.
The fact of virtual machine affection from the host side can be obtained
by reading "preemption_reported" counter via kvm entries of sysfs, but
the exact vcpu waiting time isn't reported to the host.
This patch adds this reporting.
Signed-off-by: Denis Plotnikov <den-plotnikov@xxxxxxxxxxxxxx>
---
arch/x86/include/asm/kvm_host.h | 1 +
arch/x86/kvm/debugfs.c | 17 +++++++++++++++++
Using debugfs is undesirable, as it's (a) not ABI and (b) not guaranteed to be
present as KVM (correctly) ignores debugfs setup errors.
Using debugfs is also unnecessary. The total steal time is available in guest
memory, and by definition that memory is shared with the host. To query total
steal time from userspace, use MSR filtering to trap writes (and reflect writes
back into KVM) so that the GPA of the steal time structure is known, and then
simply read the actual steal time from guest memory as needed.
Thanks for the reply!
Just to clarify, by reading the actual steal time from guest memory do you
mean by using some kind of new vcpu ioctl?
No, I mean by using the host userspace VMA to read the memory.
Oh, I think I got your idea. You mean
using KVM_CAP_X86_MSR_FILTER which...
"In combination with KVM_CAP_X86_USER_SPACE_MSR, this allows user space
to trap and emulate MSRs ..."
And then having guest's steal time struct valid address read the value
from userspace VMM like qemu directly.
Thanks for the answers!
Best,
Denis
