On 07/11/2018 08:36 PM, Paul E. McKenney wrote: > On Wed, Jul 11, 2018 at 11:20:53AM -0700, Paul E. McKenney wrote: >> On Wed, Jul 11, 2018 at 07:01:01PM +0100, David Woodhouse wrote: >>> From: David Woodhouse <dwmw@xxxxxxxxxxxx> >>> >>> RCU can spend long periods of time waiting for a CPU which is actually in >>> KVM guest mode, entirely pointlessly. Treat it like the idle and userspace >>> modes, and don't wait for it. >>> >>> Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx> >> >> And idiot here forgot about some of the debugging code in RCU's dyntick-idle >> code. I will reply with a fixed patch. >> >> The code below works just fine as long as you don't enable CONFIG_RCU_EQS_DEBUG, >> so should be OK for testing, just not for mainline. > > And here is the updated code that allegedly avoids splatting when run with > CONFIG_RCU_EQS_DEBUG. > > Thoughts? > > Thanx, Paul > > ------------------------------------------------------------------------ > > commit 12cd59e49cf734f907f44b696e2c6e4b46a291c3 > Author: David Woodhouse <dwmw@xxxxxxxxxxxx> > Date: Wed Jul 11 19:01:01 2018 +0100 > > kvm/x86: Inform RCU of quiescent state when entering guest mode > > RCU can spend long periods of time waiting for a CPU which is actually in > KVM guest mode, entirely pointlessly. Treat it like the idle and userspace > modes, and don't wait for it. > > Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx> > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> > [ paulmck: Adjust to avoid bad advice I gave to dwmw, avoid WARN_ON()s. ] > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 0046aa70205a..b0c82f70afa7 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -7458,7 +7458,9 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) > vcpu->arch.switch_db_regs &= ~KVM_DEBUGREG_RELOAD; > } > > + rcu_kvm_enter(); > kvm_x86_ops->run(vcpu); > + rcu_kvm_exit(); As indicated in my other mail. This is supposed to be handled in the guest_enter|exit_ calls around the run function. This would also handle other architectures. So if the guest_enter_irqoff code is not good enough, we should rather fix that instead of adding another rcu hint.
