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KVM: Expose the initial start value in grow_halt_poll_ns() as a module parameter

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The hard-coded value 10000 in grow_halt_poll_ns() stands for the initial
start value when raising up vcpu->halt_poll_ns.
It actually sets the first timeout to the first polling session.
This value has significant effect on how tolerant we are to outliers.
On the standard case, higher value is better - we will spend more time
in the polling busyloop, handle events/interrupts faster and result
in better performance.
But on outliers it puts us in a busy loop that does nothing.
Even if the shrink factor is zero, we will still waste time on the first
iteration.
The optimal value changes between different workloads. It depends on
outliers rate and polling sessions length.
As this value has significant effect on the dynamic halt-polling
algorithm, it should be configurable and exposed.

Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Reviewed-by: Liran Alon <liran.alon@oracle.com>
Signed-off-by: Nir Weiner <nir.weiner@oracle.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Nir Weiner
2019-01-27 12:17:15 +02:00
committed by Paolo Bonzini
parent 7fa08e71b4
commit 49113d360b
4 changed files with 31 additions and 18 deletions
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include/linux/kvm_host.h
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@@ -1203,6 +1203,7 @@ extern bool kvm_rebooting;
extern unsigned int halt_poll_ns;
extern unsigned int halt_poll_ns_grow;
extern unsigned int halt_poll_ns_grow_start;
extern unsigned int halt_poll_ns_shrink;
struct kvm_device {