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cpuidle: haltpoll: allow force loading on hosts without the REALTIME hint

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Before commit 1328edca4a ("cpuidle-haltpoll: Enable kvm guest polling
when dedicated physical CPUs are available") the cpuidle-haltpoll driver
could also be used in scenarios when the host does not advertise the
KVM_HINTS_REALTIME hint.

While the behavior introduced by the aforementioned commit makes sense as
the default there are cases where the old behavior is desired, for example,
when other kernel changes triggered by presence by this hint are unwanted,
for some workloads where the latency benefit from polling overweights the
loss from idle CPU capacity that otherwise would be available, or just when
running under older Qemu versions that lack this hint.

Let's provide a typical "force" module parameter that allows restoring the
old behavior.

Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
Reviewed-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
This commit is contained in:
Maciej S. Szmigiero 2020-03-04 12:32:48 +01:00 committed by Rafael J. Wysocki
parent 317e5ec3ec
commit dd52551fb7
1 changed files with 10 additions and 2 deletions
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12
drivers/cpuidle/cpuidle-haltpoll.c
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@ -18,6 +18,10 @@
#include <linux/kvm_para.h>
#include <linux/cpuidle_haltpoll.h>
static bool force __read_mostly;
module_param(force, bool, 0444);
MODULE_PARM_DESC(force, "Load unconditionally");
static struct cpuidle_device __percpu *haltpoll_cpuidle_devices;
static enum cpuhp_state haltpoll_hp_state;
@ -90,6 +94,11 @@ static void haltpoll_uninit(void)
haltpoll_cpuidle_devices = NULL;
}
static bool haltpool_want(void)
{
return kvm_para_has_hint(KVM_HINTS_REALTIME) || force;
}
static int __init haltpoll_init(void)
{
int ret;
@ -101,8 +110,7 @@ static int __init haltpoll_init(void)
cpuidle_poll_state_init(drv);
if (!kvm_para_available() ||
!kvm_para_has_hint(KVM_HINTS_REALTIME))
if (!kvm_para_available() || !haltpool_want())
return -ENODEV;
ret = cpuidle_register_driver(drv);