| Message ID | 20200304113248.1143057-1-mail@maciej.szmigiero.name (mailing list archive) |
|---|---|
| State | Mainlined, archived |
| Headers | show |
| Series | [v2] cpuidle-haltpoll: allow force loading on hosts without the REALTIME hint | expand |
On Wed, Mar 04, 2020 at 12:32:48PM +0100, Maciej S. Szmigiero wrote: > From: "Maciej S. Szmigiero" <maciej.szmigiero@oracle.com> > > Before commit 1328edca4a14 ("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> > --- > drivers/cpuidle/cpuidle-haltpoll.c | 12 ++++++++++-- > 1 file changed, 10 insertions(+), 2 deletions(-) > > Changes from v1: > Make the module parameter description more general, don't unnecessarily > break a line in haltpoll_init(). > > diff --git a/drivers/cpuidle/cpuidle-haltpoll.c b/drivers/cpuidle/cpuidle-haltpoll.c > index b0ce9bc78113..db124bc1ca2c 100644 > --- a/drivers/cpuidle/cpuidle-haltpoll.c > +++ b/drivers/cpuidle/cpuidle-haltpoll.c > @@ -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); Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
On Thu, Mar 12, 2020 at 5:36 PM Marcelo Tosatti <mtosatti@redhat.com> wrote: > > On Wed, Mar 04, 2020 at 12:32:48PM +0100, Maciej S. Szmigiero wrote: > > From: "Maciej S. Szmigiero" <maciej.szmigiero@oracle.com> > > > > Before commit 1328edca4a14 ("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> > > --- > > drivers/cpuidle/cpuidle-haltpoll.c | 12 ++++++++++-- > > 1 file changed, 10 insertions(+), 2 deletions(-) > > > > Changes from v1: > > Make the module parameter description more general, don't unnecessarily > > break a line in haltpoll_init(). > > > > diff --git a/drivers/cpuidle/cpuidle-haltpoll.c b/drivers/cpuidle/cpuidle-haltpoll.c > > index b0ce9bc78113..db124bc1ca2c 100644 > > --- a/drivers/cpuidle/cpuidle-haltpoll.c > > +++ b/drivers/cpuidle/cpuidle-haltpoll.c > > @@ -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); > > Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com> I'm taking this as a Reviewed-by, thanks!
On Fri, Mar 13, 2020 at 6:49 PM Rafael J. Wysocki <rafael@kernel.org> wrote: > > On Thu, Mar 12, 2020 at 5:36 PM Marcelo Tosatti <mtosatti@redhat.com> wrote: > > > > On Wed, Mar 04, 2020 at 12:32:48PM +0100, Maciej S. Szmigiero wrote: > > > From: "Maciej S. Szmigiero" <maciej.szmigiero@oracle.com> > > > > > > Before commit 1328edca4a14 ("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> > > > --- > > > drivers/cpuidle/cpuidle-haltpoll.c | 12 ++++++++++-- > > > 1 file changed, 10 insertions(+), 2 deletions(-) > > > > > > Changes from v1: > > > Make the module parameter description more general, don't unnecessarily > > > break a line in haltpoll_init(). > > > > > > diff --git a/drivers/cpuidle/cpuidle-haltpoll.c b/drivers/cpuidle/cpuidle-haltpoll.c > > > index b0ce9bc78113..db124bc1ca2c 100644 > > > --- a/drivers/cpuidle/cpuidle-haltpoll.c > > > +++ b/drivers/cpuidle/cpuidle-haltpoll.c > > > @@ -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); > > > > Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com> > > I'm taking this as a Reviewed-by, thanks! Patch applied as 5.7 material, thanks!
diff --git a/drivers/cpuidle/cpuidle-haltpoll.c b/drivers/cpuidle/cpuidle-haltpoll.c index b0ce9bc78113..db124bc1ca2c 100644 --- a/drivers/cpuidle/cpuidle-haltpoll.c +++ b/drivers/cpuidle/cpuidle-haltpoll.c @@ -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);