On Tue, 24 May 2016 09:16:03 +0800 Wanpeng Li <kernellwp@xxxxxxxxx> wrote: > 2016-05-24 8:55 GMT+08:00 yunhong jiang > <yunhong.jiang@xxxxxxxxxxxxxxx>: > > On Tue, 24 May 2016 08:53:14 +0800 > > Wanpeng Li <kernellwp@xxxxxxxxx> wrote: > > > >> 2016-05-24 6:58 GMT+08:00 yunhong jiang > >> <yunhong.jiang@xxxxxxxxxxxxxxx>: > >> > On Sun, 22 May 2016 08:21:50 +0800 > >> > Wanpeng Li <kernellwp@xxxxxxxxx> wrote: > >> > > >> >> 2016-05-21 6:06 GMT+08:00 Jiang, Yunhong > >> >> <yunhong.jiang@xxxxxxxxx>: > >> >> > > >> >> > > >> >> >> -----Original Message----- > >> >> >> From: kvm-owner@xxxxxxxxxxxxxxx > >> >> >> [mailto:kvm-owner@xxxxxxxxxxxxxxx] On Behalf Of Paolo Bonzini > >> >> >> Sent: Friday, May 20, 2016 3:34 AM > >> >> >> To: Yunhong Jiang <yunhong.jiang@xxxxxxxxxxxxxxx>; > >> >> >> kvm@xxxxxxxxxxxxxxx Cc: rkrcmar@xxxxxxxxxx > >> >> >> Subject: Re: [RFC PATCH 4/5] Utilize the vmx preemption timer > >> >> >> for tsc deadline timer > >> >> >> > >> >> >> > >> >> >> > >> >> >> On 20/05/2016 03:45, Yunhong Jiang wrote: > >> >> >> > From: Yunhong Jiang <yunhong.jiang@xxxxxxxxx> > >> >> >> > > >> >> >> > Utilizing the VMX preemption timer for tsc deadline timer > >> >> >> > virtualization. The VMX preemption timer is armed when the > >> >> >> > vCPU is running, and a VMExit will happen if the virtual > >> >> >> > TSC deadline timer expires. > >> >> >> > > >> >> >> > When the vCPU thread is scheduled out, the tsc deadline > >> >> >> > timer virtualization will be switched to use the current > >> >> >> > solution, i.e. use the timer for it. It's switched back to > >> >> >> > VMX preemption timer when the vCPU thread is scheduled int. > >> >> >> > > >> >> >> > This solution avoids the complex OS's hrtimer system, and > >> >> >> > also the host timer interrupt handling cost, with a > >> >> >> > preemption_timer VMexit. It fits well for some NFV usage > >> >> >> > scenario, when the vCPU is bound to a pCPU and the pCPU is > >> >> >> > isolated, or some similar scenario. > >> >> >> > > >> >> >> > However, it possibly has impact if the vCPU thread is > >> >> >> > scheduled in/out very frequently, because it switches > >> >> >> > from/to the hrtimer emulation a lot. > >> >> >> > > >> >> >> > Signed-off-by: Yunhong Jiang <yunhong.jiang@xxxxxxxxx> > >> >> >> > --- > >> >> >> > arch/x86/kvm/lapic.c | 108 > >> >> >> +++++++++++++++++++++++++++++++++++++++++++++++++-- > >> >> >> > arch/x86/kvm/lapic.h | 10 +++++ > >> >> >> > arch/x86/kvm/vmx.c | 26 +++++++++++++ > >> >> >> > arch/x86/kvm/x86.c | 6 +++ > >> >> >> > 4 files changed, 147 insertions(+), 3 deletions(-) > >> >> >> > > >> >> >> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > >> >> >> > index 5776473be362..a613bcfda59a 100644 > >> >> >> > --- a/arch/x86/kvm/x86.c > >> >> >> > +++ b/arch/x86/kvm/x86.c > >> >> >> > @@ -6608,6 +6608,8 @@ static int vcpu_enter_guest(struct > >> >> >> > kvm_vcpu > >> >> >> *vcpu) > >> >> >> > > >> >> >> > local_irq_disable(); > >> >> >> > > >> >> >> > + inject_expired_hwemul_timer(vcpu); > >> >> >> > >> >> >> Is this really fast enough (and does it trigger often enough) > >> >> >> that it is worth slowing down all vmenters? > >> >> >> > >> >> >> I'd rather call inject_expired_hwemul_timer from the > >> >> >> preemption timer vmexit handler instead. > >> >> >> inject_pending_hwemul_timer will set the preemption timer > >> >> >> countdown to zero if the deadline of the guest LAPIC timer > >> >> >> has passed already. This should be relatively rare. > >> >> > > >> >> > Sure and will take this way on the new patch set. I'd give > >> >> > some reson why it's this way now. Originally this patch was > >> >> > for cyclictest on guest with latency less than 15us for 24 > >> >> > hours. So, if the timer expires already before VM entry, we > >> >> > try to inject it immediately, instead of waiting for an extra > >> >> > VMExit, which may be 4~5 us. > >> >> > >> >> inject_expired_hwemul_timer() just set the pending bit, and > >> >> still need a vmexit to final exit to vcpu_run() which is the > >> >> only place to check pending and inject APIC_LVTT, so why add > >> >> inject_expired_hwemul_timer() in vcpu_enter_guest() can avoid an > >> >> extra vmexit? > >> > > >> > The inject_expired_hwemul_timer() will invoke the > >> > kvm_make_request(), which will cause the kvm try to inject the > >> > timer interrupt directly. Please notice the vcpu_enter_guest() > >> > will recheck the requests late. > >> > >> Actually I did't find another place inject pending timer irqs > >> except in vcpu_run, though kvm_set_pending_timer mention that > >> there is implicitly checked in vcpu_enter_guest. > > > > Hi, Wanpeng, thanks for the check. Please have a look on the > > changes to the arch/x86/kvm/x86.c on the patch, the > > inject_expired_hwemul_timer() is called twice there. > > Yes. > > > > > Of course, per Paolo's review, this code path will be removed on > > the next submission. > > So my question still is why there is no timer irqs inject in > vcpu_enter_guest, though kvm_set_pending_timer mention that there is > implicitly checked in vcpu_enter_guest. Do you mean the code at http://lxr.free-electrons.com/source/arch/x86/kvm/x86.c#L6607 ? It will check if ther are any event and if yes, it will exit. --jyh > > Ping Paolo, ;-) > > Regards, > Wanpeng Li -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
