From: Wanpeng Li <kernellwp@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
Pan Xinhui <xinhui.pan@linux.vnet.ibm.com>,
linux-s390 <linux-s390@vger.kernel.org>,
Davidlohr Bueso <dave@stgolabs.net>,
mpe@ellerman.id.au, boqun.feng@gmail.com, will.deacon@arm.com,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Waiman Long <waiman.long@hpe.com>,
virtualization@lists.linux-foundation.org,
Ingo Molnar <mingo@redhat.com>, Paul Mackerras <paulus@samba.org>,
benh@kernel.crashing.org, schwidefsky@de.ibm.com,
Paul McKenney <paulmck@linux.vnet.ibm.com>,
linuxppc-dev@lists.ozlabs.org, kvm <kvm@vger.kernel.org>
Subject: Re: [PATCH v2 0/4] implement vcpu preempted check
Date: Thu, 7 Jul 2016 18:27:26 +0800 [thread overview]
Message-ID: <CANRm+CxKVqrFB-cRPEvmUamZ5Y8cOGe3pyc0LMJy0t9_jo+i0Q@mail.gmail.com> (raw)
In-Reply-To: <CANRm+CyrPbOVpJ6-Wa=g6oXTU0vVfw-ciLgm-duZeVF6MBH=RA@mail.gmail.com>
2016-07-07 18:12 GMT+08:00 Wanpeng Li <kernellwp@gmail.com>:
> 2016-07-07 17:42 GMT+08:00 Peter Zijlstra <peterz@infradead.org>:
>> On Thu, Jul 07, 2016 at 04:48:05PM +0800, Wanpeng Li wrote:
>>> 2016-07-06 20:28 GMT+08:00 Paolo Bonzini <pbonzini@redhat.com>:
>>> > Hmm, you're right. We can use bit 0 of struct kvm_steal_time's flags to
>>> > indicate that pad[0] is a "VCPU preempted" field; if pad[0] is 1, the
>>> > VCPU has been scheduled out since the last time the guest reset the bit.
>>> > The guest can use an xchg to test-and-clear it. The bit can be
>>> > accessed at any time, independent of the version field.
>>>
>>> If one vCPU is preempted, and guest check it several times before this
>>> vCPU is scheded in, then the first time we can get "vCPU is
>>> preempted", however, since the field is cleared, the second time we
>>> will get "vCPU is running".
>>>
>>> Do you mean we should call record_steal_time() in both kvm_sched_in()
>>> and kvm_sched_out() to record this field? Btw, if we should keep both
>>> vcpu->preempted and kvm_steal_time's "vCPU preempted" field present
>>> simultaneous?
>>
>> I suspect you want something like so; except this has holes in.
>>
>> We clear KVM_ST_PAD_PREEMPT before disabling preemption and we set it
>> after enabling it, this means that if we get preempted in between, the
>> vcpu is reported as running even though it very much is not.
>
> Paolo also point out this to me offline yesterday: "Please change
> pad[12] to "__u32 preempted; __u32 pad[11];" too, and remember to
> update Documentation/virtual/kvm/msr.txt!". Btw, do this in preemption
> notifier means that the vCPU is real preempted on host, however,
> depends on vmexit is different semantic I think.
In addition, I see xen's vcpu_runstate_info::state is updated during
schedule, so I think I can do this similarly through kvm preemption
notifier. IIUC, xen hypervisor has VCPUOP_get_runstate_info hypercall
implemention, so the desired interface can be implemented if they add
hypercall callsite in domU. I can add hypercall to kvm similarly.
Paolo, thoughts?
Regards,
Wanpeng Li
next prev parent reply other threads:[~2016-07-07 10:27 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-28 14:43 [PATCH v2 0/4] implement vcpu preempted check Pan Xinhui
2016-06-28 14:43 ` [PATCH v2 1/4] kernel/sched: introduce vcpu preempted check interface Pan Xinhui
2016-06-28 14:43 ` [PATCH v2 2/4] powerpc/spinlock: support vcpu preempted check Pan Xinhui
2016-07-05 9:57 ` Wanpeng Li
2016-07-06 4:58 ` xinhui
2016-07-06 6:46 ` Wanpeng Li
2016-07-06 7:58 ` Peter Zijlstra
2016-07-06 8:32 ` Wanpeng Li
2016-07-06 10:18 ` xinhui
2016-07-06 10:54 ` Balbir Singh
2016-07-15 15:35 ` Pan Xinhui
2016-06-28 14:43 ` [PATCH v2 3/4] locking/osq: Drop the overload of osq_lock() Pan Xinhui
2016-06-28 14:43 ` [PATCH v2 4/4] kernel/locking: Drop the overload of {mutex,rwsem}_spin_on_owner Pan Xinhui
2016-07-06 6:52 ` [PATCH v2 0/4] implement vcpu preempted check Peter Zijlstra
2016-07-06 7:47 ` Juergen Gross
2016-07-06 8:19 ` Peter Zijlstra
2016-07-06 8:38 ` Juergen Gross
2016-07-06 12:44 ` Paolo Bonzini
2016-07-06 16:56 ` Christian Borntraeger
2016-07-06 10:05 ` xinhui
2016-07-06 10:44 ` Paolo Bonzini
2016-07-06 11:59 ` Peter Zijlstra
2016-07-06 12:08 ` Wanpeng Li
2016-07-06 12:28 ` Paolo Bonzini
2016-07-06 13:03 ` Wanpeng Li
2016-07-07 8:48 ` Wanpeng Li
2016-07-07 9:42 ` Peter Zijlstra
2016-07-07 10:12 ` Wanpeng Li
2016-07-07 10:27 ` Wanpeng Li [this message]
2016-07-07 11:15 ` Peter Zijlstra
2016-07-07 11:08 ` Peter Zijlstra
2016-07-07 11:09 ` Peter Zijlstra
2016-07-07 11:21 ` Peter Zijlstra
2016-07-11 15:10 ` Waiman Long
2016-07-12 4:16 ` Juergen Gross
2016-07-12 18:16 ` Waiman Long
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