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. 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
