Hi Alejadnro,
On 2/15/2024 9:31 PM, Alejandro Jimenez wrote:
The goal of this RFC is to agree on a mechanism for querying the state (and
related stats) of APICv/AVIC. I clearly have an AVIC bias when approaching this
topic since that is the side that I have mostly looked at, and has the greater
number of possible inhibits, but I believe the argument applies for both
vendor's technologies.
Currently, a user or monitoring app trying to determine if APICv is actually
being used needs implementation-specific knowlegde in order to look for specific
types of #VMEXIT (i.e. AVIC_INCOMPLETE_IPI/AVIC_NOACCEL), checking GALog events
by watching /proc/interrupts for AMD-Vi*-GA, etc. There are existing tracepoints
(e.g. kvm_apicv_accept_irq, kvm_avic_ga_log) that make this task easier, but
tracefs is not viable in some scenarios. Adding kvm debugfs entries has similar
downsides. Suravee has previously proposed a new IOCTL interface[0] to expose
this information, but there has not been any development in that direction.
Sean has mentioned a preference for using BPF to extract info from the current
tracepoints, which would require reworking existing structs to access some
desired data, but as far as I know there isn't any work done on that approach
yet.
Recently Joao mentioned another alternative: the binary stats framework that is
already supported by kernel[1] and QEMU[2]. This RFC has minimal code changes to
expose the relevant info based on the existing data types the framework already
supports. If there is consensus on using this approach, I can expand the fd
stats subsystem to include other data types (e.g. a bitmap type for exposing the
inhibit reasons), as well as adding documentation on KVM explaining which stats
are relevant for APICv and how to query them.
Thanks for the series. IMO this approach makes sense. May be we should
consider adding one more stat to say whether AVIC is active or not. That
way,
Check whether AVIC is active or not.
If AVIC is active, then inhibited or not
If not inhibited, then use other statistics info.
I have reviewed/tested this series on AMD Genoa platform. It looks good
to me.
Reviewed-by: Vasant Hegde <vasant.hegde@xxxxxxx>
-Vasant
A basic example of retrieving the stats via qmp-shell, showing both a VM and
per-vCPU case:
# /usr/local/bin/qmp-shell --pretty ./qmp-sock
(QEMU) query-stats target=vm providers=[{'provider':'kvm','names':['apicv_inhibited']}]
{
"return": [
{
"provider": "kvm",
"stats": [
{
"name": "apicv_inhibited",
"value": false
}
]
}
]
}
(QEMU) query-stats target=vcpu vcpus=['/machine/unattached/device[0]'] providers=[{'provider':'kvm','names':['apicv_accept_irq','ga_log_event']}]
{
"return": [
{
"provider": "kvm",
"qom-path": "/machine/unattached/device[0]",
"stats": [
{
"name": "ga_log_event",
"value": 98
},
{
"name": "apicv_accept_irq",
"value": 166920
}
]
}
]
}
If other alternatives are preferred, please let's use this thread to discuss and
I can take a shot at implementing the desired solution.
Regards,
Alejandro
[0] https://lore.kernel.org/qemu-devel/7e0d22fa-b9b0-ad1a-3a37-a450ec5d73e8@xxxxxxx/
[1] https://lore.kernel.org/all/20210618222709.1858088-1-jingzhangos@xxxxxxxxxx/
[2] https://lore.kernel.org/qemu-devel/20220530150714.756954-1-pbonzini@xxxxxxxxxx/
Alejandro Jimenez (3):
x86: KVM: stats: Add a stat to report status of APICv inhibition
x86: KVM: stats: Add stat counter for IRQs injected via APICv
x86: KVM: stats: Add a stat counter for GALog events
arch/x86/include/asm/kvm_host.h | 3 +++
arch/x86/kvm/svm/avic.c | 4 +++-
arch/x86/kvm/svm/svm.c | 3 +++
arch/x86/kvm/vmx/vmx.c | 2 ++
arch/x86/kvm/x86.c | 12 +++++++++++-
5 files changed, 22 insertions(+), 2 deletions(-)
base-commit: 7455665a3521aa7b56245c0a2810f748adc5fdd4
