From: Paolo Bonzini <pbonzini@redhat.com>
To: David Vrabel <david.vrabel@citrix.com>, Waiman Long <Waiman.Long@hp.com>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>,
Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>,
Peter Zijlstra <peterz@infradead.org>,
virtualization@lists.linux-foundation.org,
Andi Kleen <andi@firstfloor.org>,
"H. Peter Anvin" <hpa@zytor.com>,
Michel Lespinasse <walken@google.com>,
Alok Kataria <akataria@vmware.com>,
linux-arch@vger.kernel.org, x86@kernel.org,
Ingo Molnar <mingo@redhat.com>,
Scott J Norton <scott.norton@hp.com>,
xen-devel@lists.xenproject.org,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Alexander Fyodorov <halcy@yandex.ru>,
Rik van Riel <riel@redhat.com>, Arnd Bergmann <arnd@arndb.de>,
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
Daniel J Blueman <daniel@numascale.com>,
Oleg Nesterov <oleg@redhat.com>,
Steven Rostedt <rostedt@goodmis.org>,
Chris Wright <chrisw@sous-sol.org>,
George Spelvin <linux@horizon.com>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH RFC v5 7/8] pvqspinlock, x86: Add qspinlock para-virtualization support
Date: Thu, 27 Feb 2014 14:11:03 +0100 [thread overview]
Message-ID: <530F3967.6030805@redhat.com> (raw)
In-Reply-To: <530F2B8F.1010401@citrix.com>
Il 27/02/2014 13:11, David Vrabel ha scritto:
>> > This patch adds para-virtualization support to the queue spinlock code
>> > by enabling the queue head to kick the lock holder CPU, if known,
>> > in when the lock isn't released for a certain amount of time. It
>> > also enables the mutual monitoring of the queue head CPU and the
>> > following node CPU in the queue to make sure that their CPUs will
>> > stay scheduled in.
> I'm not really understanding how this is supposed to work. There
> appears to be an assumption that a guest can keep one of its VCPUs
> running by repeatedly kicking it? This is not possible under Xen and I
> doubt it's possible under KVM or any other hypervisor.
KVM allows any VCPU to wake up a currently halted VCPU of its choice,
see Documentation/virtual/kvm/hypercalls.txt.
5. KVM_HC_KICK_CPU
------------------------
Architecture: x86
Status: active
Purpose: Hypercall used to wakeup a vcpu from HLT state
Usage example : A vcpu of a paravirtualized guest that is busywaiting
in guest kernel mode for an event to occur (ex: a spinlock to become
available) can execute HLT instruction once it has busy-waited for more
than a threshold time-interval. Execution of HLT instruction would cause
the hypervisor to put the vcpu to sleep until occurrence of an
appropriate
event. Another vcpu of the same guest can wakeup the sleeping vcpu by
issuing KVM_HC_KICK_CPU hypercall, specifying APIC ID (a1) of the vcpu
to be woken up. An additional argument (a0) is used in the hypercall for
future use.
This is the same as a dummy IPI, but cheaper (about 2000 clock cycles
wasted on the source VCPU, and the latency on the destination is about
half; an IPI costs roughly the same on the source and much more on the
destination).
It looks like Xen could use an event channel.
Paolo
next prev parent reply other threads:[~2014-02-27 13:11 UTC|newest]
Thread overview: 58+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-02-26 15:14 [PATCH v5 0/8] qspinlock: a 4-byte queue spinlock with PV support Waiman Long
2014-02-26 15:14 ` [PATCH v5 1/8] qspinlock: Introducing a 4-byte queue spinlock implementation Waiman Long
2014-02-26 16:22 ` Peter Zijlstra
2014-02-27 20:25 ` Waiman Long
2014-02-26 16:24 ` Peter Zijlstra
2014-02-27 20:25 ` Waiman Long
2014-02-26 15:14 ` [PATCH v5 2/8] qspinlock, x86: Enable x86-64 to use queue spinlock Waiman Long
2014-02-26 15:14 ` [PATCH v5 3/8] qspinlock, x86: Add x86 specific optimization for 2 contending tasks Waiman Long
2014-02-26 16:20 ` Peter Zijlstra
2014-02-27 20:42 ` Waiman Long
2014-02-28 9:29 ` Peter Zijlstra
2014-02-28 16:25 ` Linus Torvalds
2014-02-28 17:37 ` Peter Zijlstra
2014-02-28 16:38 ` Waiman Long
2014-02-28 17:56 ` Peter Zijlstra
2014-03-03 17:43 ` Peter Zijlstra
2014-03-04 15:27 ` Waiman Long
2014-03-04 16:58 ` Peter Zijlstra
2014-03-04 18:09 ` Peter Zijlstra
2014-03-04 17:48 ` Waiman Long
2014-03-04 22:40 ` Peter Zijlstra
2014-03-05 20:59 ` Peter Zijlstra
2014-02-26 15:14 ` [PATCH RFC v5 4/8] pvqspinlock, x86: Allow unfair spinlock in a real PV environment Waiman Long
2014-02-26 17:07 ` Konrad Rzeszutek Wilk
2014-02-28 17:06 ` Waiman Long
2014-03-03 10:55 ` Paolo Bonzini
2014-03-04 15:15 ` Waiman Long
2014-03-04 15:23 ` Paolo Bonzini
2014-03-04 15:39 ` David Vrabel
2014-03-04 17:50 ` Raghavendra K T
2014-02-27 12:28 ` David Vrabel
2014-02-27 19:40 ` Waiman Long
2014-02-26 15:14 ` [PATCH RFC v5 5/8] pvqspinlock, x86: Enable unfair queue spinlock in a KVM guest Waiman Long
2014-02-26 17:08 ` Konrad Rzeszutek Wilk
2014-02-28 17:08 ` Waiman Long
2014-02-27 9:41 ` Paolo Bonzini
2014-02-27 19:05 ` Waiman Long
2014-02-27 10:40 ` Raghavendra K T
2014-02-27 19:12 ` Waiman Long
2014-02-26 15:14 ` [PATCH RFC v5 6/8] pvqspinlock, x86: Rename paravirt_ticketlocks_enabled Waiman Long
2014-02-26 15:14 ` [PATCH RFC v5 7/8] pvqspinlock, x86: Add qspinlock para-virtualization support Waiman Long
2014-02-26 17:54 ` Konrad Rzeszutek Wilk
2014-02-27 12:11 ` David Vrabel
2014-02-27 13:11 ` Paolo Bonzini [this message]
2014-02-27 14:18 ` David Vrabel
2014-02-27 14:45 ` Paolo Bonzini
2014-02-27 15:22 ` Raghavendra K T
2014-02-27 15:50 ` Paolo Bonzini
2014-03-03 11:06 ` [Xen-devel] " David Vrabel
2014-02-27 20:50 ` Waiman Long
2014-02-27 19:42 ` Waiman Long
2014-02-26 15:14 ` [PATCH RFC v5 8/8] pvqspinlock, x86: Enable KVM to use qspinlock's PV support Waiman Long
2014-02-27 9:31 ` Paolo Bonzini
2014-02-27 18:36 ` Waiman Long
2014-02-26 17:00 ` [PATCH v5 0/8] qspinlock: a 4-byte queue spinlock with " Konrad Rzeszutek Wilk
2014-02-28 16:56 ` Waiman Long
2014-02-26 22:26 ` Paul E. McKenney
-- strict thread matches above, loose matches on Subject: below --
2014-02-27 4:32 Waiman Long
2014-02-27 4:32 ` [PATCH RFC v5 7/8] pvqspinlock, x86: Add qspinlock para-virtualization support Waiman Long
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