On 6/4/19 1:24 PM, Marcelo Tosatti wrote:
>
> When performing guest side polling, it is not necessary to
> also perform host side polling.
>
> So disable host side polling, via the new MSR interface,
> when loading cpuidle-haltpoll driver.
>
> Signed-off-by: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
>
> ---
>
> v2: remove extra "}"
>
> arch/x86/Kconfig | 7 +++++
> arch/x86/include/asm/cpuidle_haltpoll.h | 8 ++++++
> arch/x86/kernel/kvm.c | 40 ++++++++++++++++++++++++++++++++
> drivers/cpuidle/cpuidle-haltpoll.c | 9 ++++++-
> include/linux/cpuidle_haltpoll.h | 16 ++++++++++++
> 5 files changed, 79 insertions(+), 1 deletion(-)
>
> Index: linux-2.6.git/arch/x86/include/asm/cpuidle_haltpoll.h
> ===================================================================
> --- /dev/null 1970-01-01 00:00:00.000000000 +0000
> +++ linux-2.6.git/arch/x86/include/asm/cpuidle_haltpoll.h 2019-06-03 19:38:42.328718617 -0300
> @@ -0,0 +1,8 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _ARCH_HALTPOLL_H
> +#define _ARCH_HALTPOLL_H
> +
> +void arch_haltpoll_enable(void);
> +void arch_haltpoll_disable(void);
> +
> +#endif
> Index: linux-2.6.git/drivers/cpuidle/cpuidle-haltpoll.c
> ===================================================================
> --- linux-2.6.git.orig/drivers/cpuidle/cpuidle-haltpoll.c 2019-06-03 19:38:12.376619124 -0300
> +++ linux-2.6.git/drivers/cpuidle/cpuidle-haltpoll.c 2019-06-03 19:38:42.328718617 -0300
> @@ -15,6 +15,7 @@
> #include <linux/module.h>
> #include <linux/timekeeping.h>
> #include <linux/sched/idle.h>
> +#include <linux/cpuidle_haltpoll.h>
> #define CREATE_TRACE_POINTS
> #include "cpuidle-haltpoll-trace.h"
>
> @@ -157,11 +158,17 @@
>
> static int __init haltpoll_init(void)
> {
> - return cpuidle_register(&haltpoll_driver, NULL);
> + int ret = cpuidle_register(&haltpoll_driver, NULL);
> +
> + if (ret == 0)
> + arch_haltpoll_enable();
> +
> + return ret;
> }
>
> static void __exit haltpoll_exit(void)
> {
> + arch_haltpoll_disable();
> cpuidle_unregister(&haltpoll_driver);
> }
>
> Index: linux-2.6.git/include/linux/cpuidle_haltpoll.h
> ===================================================================
> --- /dev/null 1970-01-01 00:00:00.000000000 +0000
> +++ linux-2.6.git/include/linux/cpuidle_haltpoll.h 2019-06-03 19:41:57.293366260 -0300
> @@ -0,0 +1,16 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _CPUIDLE_HALTPOLL_H
> +#define _CPUIDLE_HALTPOLL_H
> +
> +#ifdef CONFIG_ARCH_CPUIDLE_HALTPOLL
> +#include <asm/cpuidle_haltpoll.h>
> +#else
> +static inline void arch_haltpoll_enable(void)
> +{
> +}
> +
> +static inline void arch_haltpoll_disable(void)
> +{
> +}
> +#endif
> +#endif
> Index: linux-2.6.git/arch/x86/Kconfig
> ===================================================================
> --- linux-2.6.git.orig/arch/x86/Kconfig 2019-06-03 19:38:12.376619124 -0300
> +++ linux-2.6.git/arch/x86/Kconfig 2019-06-03 19:42:34.478489868 -0300
> @@ -787,6 +787,7 @@
> bool "KVM Guest support (including kvmclock)"
> depends on PARAVIRT
> select PARAVIRT_CLOCK
> + select ARCH_CPUIDLE_HALTPOLL
> default y
> ---help---
> This option enables various optimizations for running under the KVM
> @@ -795,6 +796,12 @@
> underlying device model, the host provides the guest with
> timing infrastructure such as time of day, and system time
>
> +config ARCH_CPUIDLE_HALTPOLL
> + def_bool n
> + proUmpt "Disable host haltpoll when loading haltpoll driver"
> + help
> + If virtualized under KVM, disable host haltpoll.
> +
> config PVH
> bool "Support for running PVH guests"
> ---help---
> Index: linux-2.6.git/arch/x86/kernel/kvm.c
> ===================================================================
> --- linux-2.6.git.orig/arch/x86/kernel/kvm.c 2019-06-03 19:38:12.376619124 -0300
> +++ linux-2.6.git/arch/x86/kernel/kvm.c 2019-06-03 19:40:14.359024312 -0300
> @@ -853,3 +853,43 @@
> }
>
> #endif /* CONFIG_PARAVIRT_SPINLOCKS */
> +
> +#ifdef CONFIG_ARCH_CPUIDLE_HALTPOLL
> +
> +void kvm_disable_host_haltpoll(void *i)
> +{
> + wrmsrl(MSR_KVM_POLL_CONTROL, 0);
> +}
> +
> +void kvm_enable_host_haltpoll(void *i)
> +{
> + wrmsrl(MSR_KVM_POLL_CONTROL, 1);
> +}
> +
> +void arch_haltpoll_enable(void)
> +{
> + if (!kvm_para_has_feature(KVM_FEATURE_POLL_CONTROL))
> + return;
> +
Perhaps warn the user when failing to disable host poll e.g.:
if (!kvm_para_has_feature(KVM_FEATURE_POLL_CONTROL)) {
pr_warn_once("haltpoll: Failed to disable host halt polling\n");
return;
}
But I wonder whether we should fail to load cpuidle-haltpoll when host halt
polling can't be disabled[*]? That is to avoid polling in both host and guest
and *possibly* avoid chances for performance regressions when running on older
hypervisors?
[*] with guest still able load with lack of host polling control via modparam
> + preempt_disable();
> + /* Enabling guest halt poll disables host halt poll */
> + kvm_disable_host_haltpoll(NULL);
> + smp_call_function(kvm_disable_host_haltpoll, NULL, 1);
> + preempt_enable();
> +}
> +EXPORT_SYMBOL_GPL(arch_haltpoll_enable);
> +
> +void arch_haltpoll_disable(void)
> +{
> + if (!kvm_para_has_feature(KVM_FEATURE_POLL_CONTROL))
> + return;
> +
> + preempt_disable();
> + /* Enabling guest halt poll disables host halt poll */
> + kvm_enable_host_haltpoll(NULL);
> + smp_call_function(kvm_enable_host_haltpoll, NULL, 1);
> + preempt_enable();
> +}
> +
> +EXPORT_SYMBOL_GPL(arch_haltpoll_disable);
> +#endif
>
