| Message ID | 20230620140625.1001886-5-longman@redhat.com |
|---|---|
| State | New |
| Headers | show |
| Series | x86/speculation: Disable IBRS when idle | expand |
On Tue, Jun 20, 2023 at 10:06:24AM -0400, Waiman Long wrote: > Commit bf5835bcdb96 ("intel_idle: Disable IBRS during long idle") > disables IBRS when the cstate is 6 or lower. However, there are > some use cases where a customer may want to use max_cstate=1 to > lower latency. And then add the WRMSRs to increase latency again... Since you're mucking about with all this, perhaps see if you can measure the latency impact of all this. > Such use cases will suffer from the performance > degradation caused by the enabling of IBRS in the sibling idle thread. > Add a "no_ibrs" module parameter to force disable IBRS and the > CPUIDLE_FLAG_IRQ_ENABLE flag if set. > > In the case of a Skylake server with max_cstate=1, this new no_ibrs > option will increase the IRQ response latency as IRQ will now be > disabled. > > Signed-off-by: Waiman Long <longman@redhat.com> > --- > drivers/idle/intel_idle.c | 14 ++++++++++++-- > 1 file changed, 12 insertions(+), 2 deletions(-) > > diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c > index 07fa23707b3c..366dacccc971 100644 > --- a/drivers/idle/intel_idle.c > +++ b/drivers/idle/intel_idle.c > @@ -69,6 +69,7 @@ static int max_cstate = CPUIDLE_STATE_MAX - 1; > static unsigned int disabled_states_mask __read_mostly; > static unsigned int preferred_states_mask __read_mostly; > static bool force_irq_on __read_mostly; > +static bool no_ibrs __read_mostly; > > static struct cpuidle_device __percpu *intel_idle_cpuidle_devices; > > @@ -1907,12 +1908,15 @@ static void __init intel_idle_init_cstates_icpu(struct cpuidle_driver *drv) > WARN_ON_ONCE(state->flags & CPUIDLE_FLAG_IRQ_ENABLE); > state->enter = intel_idle_xstate; > } else if (cpu_feature_enabled(X86_FEATURE_KERNEL_IBRS) && > - state->flags & CPUIDLE_FLAG_IBRS) { > + ((state->flags & CPUIDLE_FLAG_IBRS) || no_ibrs)) { > /* > * IBRS mitigation requires that C-states are entered > * with interrupts disabled. > */ > - WARN_ON_ONCE(state->flags & CPUIDLE_FLAG_IRQ_ENABLE); > + if (no_ibrs && (state->flags & CPUIDLE_FLAG_IRQ_ENABLE)) > + state->flags &= ~CPUIDLE_FLAG_IRQ_ENABLE; > + else > + WARN_ON_ONCE(state->flags & CPUIDLE_FLAG_IRQ_ENABLE); > state->enter = intel_idle_ibrs; > } else if (state->flags & CPUIDLE_FLAG_IRQ_ENABLE) { > state->enter = intel_idle_irq; > @@ -2165,3 +2169,9 @@ MODULE_PARM_DESC(preferred_cstates, "Mask of preferred idle states"); > * 'CPUIDLE_FLAG_INIT_XSTATE' and 'CPUIDLE_FLAG_IBRS' flags. > */ > module_param(force_irq_on, bool, 0444); > +/* > + * Force the disabling of IBRS when X86_FEATURE_KERNEL_IBRS is on and > + * CPUIDLE_FLAG_IRQ_ENABLE isn't set. > + */ > +module_param(no_ibrs, bool, 0444); > +MODULE_PARM_DESC(no_ibrs, "Disable IBRS when idle"); Urgghhh.. the flag is CPUIDLE_FLAG_IBRS, so "no_ibrs" implies clearing that flag.
diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c index 07fa23707b3c..366dacccc971 100644 --- a/drivers/idle/intel_idle.c +++ b/drivers/idle/intel_idle.c @@ -69,6 +69,7 @@ static int max_cstate = CPUIDLE_STATE_MAX - 1; static unsigned int disabled_states_mask __read_mostly; static unsigned int preferred_states_mask __read_mostly; static bool force_irq_on __read_mostly; +static bool no_ibrs __read_mostly; static struct cpuidle_device __percpu *intel_idle_cpuidle_devices; @@ -1907,12 +1908,15 @@ static void __init intel_idle_init_cstates_icpu(struct cpuidle_driver *drv) WARN_ON_ONCE(state->flags & CPUIDLE_FLAG_IRQ_ENABLE); state->enter = intel_idle_xstate; } else if (cpu_feature_enabled(X86_FEATURE_KERNEL_IBRS) && - state->flags & CPUIDLE_FLAG_IBRS) { + ((state->flags & CPUIDLE_FLAG_IBRS) || no_ibrs)) { /* * IBRS mitigation requires that C-states are entered * with interrupts disabled. */ - WARN_ON_ONCE(state->flags & CPUIDLE_FLAG_IRQ_ENABLE); + if (no_ibrs && (state->flags & CPUIDLE_FLAG_IRQ_ENABLE)) + state->flags &= ~CPUIDLE_FLAG_IRQ_ENABLE; + else + WARN_ON_ONCE(state->flags & CPUIDLE_FLAG_IRQ_ENABLE); state->enter = intel_idle_ibrs; } else if (state->flags & CPUIDLE_FLAG_IRQ_ENABLE) { state->enter = intel_idle_irq; @@ -2165,3 +2169,9 @@ MODULE_PARM_DESC(preferred_cstates, "Mask of preferred idle states"); * 'CPUIDLE_FLAG_INIT_XSTATE' and 'CPUIDLE_FLAG_IBRS' flags. */ module_param(force_irq_on, bool, 0444); +/* + * Force the disabling of IBRS when X86_FEATURE_KERNEL_IBRS is on and + * CPUIDLE_FLAG_IRQ_ENABLE isn't set. + */ +module_param(no_ibrs, bool, 0444); +MODULE_PARM_DESC(no_ibrs, "Disable IBRS when idle");
Commit bf5835bcdb96 ("intel_idle: Disable IBRS during long idle") disables IBRS when the cstate is 6 or lower. However, there are some use cases where a customer may want to use max_cstate=1 to lower latency. Such use cases will suffer from the performance degradation caused by the enabling of IBRS in the sibling idle thread. Add a "no_ibrs" module parameter to force disable IBRS and the CPUIDLE_FLAG_IRQ_ENABLE flag if set. In the case of a Skylake server with max_cstate=1, this new no_ibrs option will increase the IRQ response latency as IRQ will now be disabled. Signed-off-by: Waiman Long <longman@redhat.com> --- drivers/idle/intel_idle.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-)