Default halt_poll_ns_shrink value of 0 always resets polling interval
to 0 on an un-successful poll where vcpu wakeup is not received. This is
mostly to avoid pointless polling for more number of shorter intervals. But
disabled shrink assumes vcpu wakeup is less likely to be received in
subsequent shorter polling intervals. Another side effect of 0 shrink value
is that, even on a successful poll if total block time was greater than
current polling interval, the polling interval starts over from 0 instead
of shrinking by a factor.
Enabling shrink with value of 2 allows the polling interval to gradually
decrement in case of un-successful poll events as well. This gives a fair
chance for successful polling events in subsequent polling intervals rather
than resetting it to 0 and starting over from grow_start.
Below kvm stat log snippet shows interleaved growth and shrinking of
polling interval:
87162647182125: kvm_halt_poll_ns: vcpu 0: halt_poll_ns 10000 (grow 0)
87162647637763: kvm_halt_poll_ns: vcpu 0: halt_poll_ns 20000 (grow 10000)
87162649627943: kvm_halt_poll_ns: vcpu 0: halt_poll_ns 40000 (grow 20000)
87162650892407: kvm_halt_poll_ns: vcpu 0: halt_poll_ns 20000 (shrink 40000)
87162651540378: kvm_halt_poll_ns: vcpu 0: halt_poll_ns 40000 (grow 20000)
87162652276768: kvm_halt_poll_ns: vcpu 0: halt_poll_ns 20000 (shrink 40000)
87162652515037: kvm_halt_poll_ns: vcpu 0: halt_poll_ns 40000 (grow 20000)
87162653383787: kvm_halt_poll_ns: vcpu 0: halt_poll_ns 20000 (shrink 40000)
87162653627670: kvm_halt_poll_ns: vcpu 0: halt_poll_ns 10000 (shrink 20000)
87162653796321: kvm_halt_poll_ns: vcpu 0: halt_poll_ns 20000 (grow 10000)
87162656171645: kvm_halt_poll_ns: vcpu 0: halt_poll_ns 10000 (shrink 20000)
87162661607487: kvm_halt_poll_ns: vcpu 0: halt_poll_ns 0 (shrink 10000)
Having both grow and shrink enabled creates a balance in polling interval
growth and shrink behavior. Tests show improved successful polling attempt
ratio which contribute to VM performance. Power penalty is quite negligible
as shrunk polling intervals create bursts of very short durations.
Performance assessment results show 3-6% improvements in CPU+GPU, Memory
and Storage Android VM workloads whereas 5-9% improvement in average FPS of
gaming VM workloads.
Power penalty is below 1% where host OS is either idle or running a
native workload having 2 VMs enabled. CPU/GPU intensive gaming workloads
as well do not show any increased power overhead with shrink enabled.
Co-developed-by: Rajendran Jaishankar <jaishankar.rajendran@intel.com>
Signed-off-by: Rajendran Jaishankar <jaishankar.rajendran@intel.com>
Signed-off-by: Parshuram Sangle <parshuram.sangle@intel.com>
Link: https://lore.kernel.org/r/20231102154628.2120-2-parshuram.sangle@intel.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Module parameters are in sysfs, not debugfs, so change that.
Remove superfluous "that" following "Note:".
Hyphenate "system-wide" values.
Hyphenate "trade-off".
Don't treat "denial of service" as a verb.
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Suraj Jitindar Singh <sjitindarsingh@gmail.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: kvm@vger.kernel.org
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20230612030810.23376-2-rdunlap@infradead.org
Clarify the existing documentation about how KVM_CAP_HALT_POLL and
halt_poll_ns interact to make it clear that VMs using KVM_CAP_HALT_POLL
ignore halt_poll_ns.
Signed-off-by: David Matlack <dmatlack@google.com>
Message-Id: <20221201195249.3369720-3-dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Move halt-polling.rst into the common KVM documentation directory and
out of the x86-specific directory. Halt-polling is a common feature and
the existing documentation is already written as such.
Signed-off-by: David Matlack <dmatlack@google.com>
Message-Id: <20221201195249.3369720-2-dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
ARM already has an arm/ subdirectory, but s390 and x86 do not even though
they have a relatively large number of files specific to them. Create
new directories in Documentation/virt/kvm for these two architectures
as well.
While at it, group the API documentation and the developer documentation
in the table of contents.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20220322110712.222449-2-pbonzini@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
- Fix document title to match ReST format
- Convert the table to be properly recognized
- Some indentation fixes to match ReST syntax.
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
