diff options
| author | Leonardo Bras <leobras@redhat.com> | 2024-05-10 23:05:56 -0300 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2024-09-04 10:44:42 -0400 |
| commit | 593377036e50de89132bc1222800174fde0780ec (patch) | |
| tree | 84cfe3462a8af2675378fe39427c479587cded1f | |
| parent | d30d9ee94cc0e7ae91da7251d9c280b8cf7e5e4d (diff) | |
kvm: Note an RCU quiescent state on guest exit
As of today, KVM notes a quiescent state only in guest entry, which is good
as it avoids the guest being interrupted for current RCU operations.
While the guest vcpu runs, it can be interrupted by a timer IRQ that will
check for any RCU operations waiting for this CPU. In case there are any of
such, it invokes rcu_core() in order to sched-out the current thread and
note a quiescent state.
This occasional schedule work will introduce tens of microsseconds of
latency, which is really bad for vcpus running latency-sensitive
applications, such as real-time workloads.
So, note a quiescent state in guest exit, so the interrupted guests is able
to deal with any pending RCU operations before being required to invoke
rcu_core(), and thus avoid the overhead of related scheduler work.
Signed-off-by: Leonardo Bras <leobras@redhat.com>
Acked-by: Paul E. McKenney <paulmck@kernel.org>
Acked-by: Sean Christopherson <seanjc@google.com>
Message-ID: <20240511020557.1198200-1-leobras@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
| -rw-r--r-- | include/linux/context_tracking.h | 6 | ||||
| -rw-r--r-- | include/linux/kvm_host.h | 10 |
2 files changed, 13 insertions, 3 deletions
diff --git a/include/linux/context_tracking.h b/include/linux/context_tracking.h index 6e76b9dba00e..8a78fabeafc3 100644 --- a/include/linux/context_tracking.h +++ b/include/linux/context_tracking.h @@ -80,10 +80,12 @@ static __always_inline bool context_tracking_guest_enter(void) return context_tracking_enabled_this_cpu(); } -static __always_inline void context_tracking_guest_exit(void) +static __always_inline bool context_tracking_guest_exit(void) { if (context_tracking_enabled()) __ct_user_exit(CONTEXT_GUEST); + + return context_tracking_enabled_this_cpu(); } #define CT_WARN_ON(cond) WARN_ON(context_tracking_enabled() && (cond)) @@ -98,7 +100,7 @@ static inline void exception_exit(enum ctx_state prev_ctx) { } static inline int ct_state(void) { return -1; } static inline int __ct_state(void) { return -1; } static __always_inline bool context_tracking_guest_enter(void) { return false; } -static __always_inline void context_tracking_guest_exit(void) { } +static __always_inline bool context_tracking_guest_exit(void) { return false; } #define CT_WARN_ON(cond) do { } while (0) #endif /* !CONFIG_CONTEXT_TRACKING_USER */ diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index b23c6d48392f..0d5125a3e31a 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -485,7 +485,15 @@ static __always_inline void guest_state_enter_irqoff(void) */ static __always_inline void guest_context_exit_irqoff(void) { - context_tracking_guest_exit(); + /* + * Guest mode is treated as a quiescent state, see + * guest_context_enter_irqoff() for more details. + */ + if (!context_tracking_guest_exit()) { + instrumentation_begin(); + rcu_virt_note_context_switch(); + instrumentation_end(); + } } /* |