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xen-devel
[Xen-devel] Re: [PATCH RFC V2 5/5] kvm guest : pv-ticketlocks support fo
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To: |
Raghavendra K T <raghukt@xxxxxxxxxxxxxxxxxx> |
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Subject: |
[Xen-devel] Re: [PATCH RFC V2 5/5] kvm guest : pv-ticketlocks support for linux guests running on KVM hypervisor |
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From: |
Jeremy Fitzhardinge <jeremy@xxxxxxxx> |
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Date: |
Wed, 26 Oct 2011 12:46:15 -0700 |
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Cc: |
"x86@xxxxxxxxxx" <x86@xxxxxxxxxx>, KVM <kvm@xxxxxxxxxxxxxxx>, Stefano Stabellini <Stefano.Stabellini@xxxxxxxxxxxxx>, Peter Zijlstra <peterz@xxxxxxxxxxxxx>, Virtualization <virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx>, "H. Peter Anvin" <hpa@xxxxxxxxx>, Xen <xen-devel@xxxxxxxxxxxxxxxxxxx>, Dave Jiang <dave.jiang@xxxxxxxxx>, Gleb Natapov <gleb@xxxxxxxxxx>, Raghavendra K T <raghavendra.kt@xxxxxxxxxxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, Avi Kivity <avi@xxxxxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, Srivatsa Vaddagiri <vatsa@xxxxxxxxxxxxxxxxxx>, Sedat Dilek <sedat.dilek@xxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, Yinghai Lu <yinghai@xxxxxxxxxx>, Greg Kroah-Hartman <gregkh@xxxxxxx>, Marcelo Tosatti <mtosatti@xxxxxxxxxx>, LKML <linux-kernel@xxxxxxxxxxxxxxx>, Suzuki Poulose <suzuki@xxxxxxxxxxxxxxxxxx> |
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Thu, 27 Oct 2011 05:06:37 -0700 |
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<20111023190307.16364.35381.sendpatchset@xxxxxxxxxxxxxxxxxxxx> <20111023190753.16364.31164.sendpatchset@xxxxxxxxxxxxxxxxxxxx> <4EA7012B.5040808@xxxxxxxx> <4EA85E32.3080107@xxxxxxxxxxxxxxxxxx> |
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On 10/26/2011 12:23 PM, Raghavendra K T wrote:
> On 10/26/2011 12:04 AM, Jeremy Fitzhardinge wrote:
>> On 10/23/2011 12:07 PM, Raghavendra K T wrote:
>>> This patch extends Linux guests running on KVM hypervisor to support
>>> +/*
>>> + * Setup pv_lock_ops to exploit KVM_FEATURE_WAIT_FOR_KICK if present.
>>> + * This needs to be setup really early in boot, before the first
>>> call to
>>> + * spinlock is issued!
>>
>> Actually, it doesn't matter that much. The in-memory format is the same
>> for regular and PV spinlocks, and the PV paths only come into play if
>> the "slowpath" flag is set in the lock, which it never will be by the
>> non-PV code.
>>
>> In principle, you could defer initializing PV ticketlocks until some
>> arbitrarily late point if you notice that the system is oversubscribed
>> enough to require it.
>
> ok.. so this means it will not affect even if it is initialized in
> middle somewhere, but better to do it before we start seeing lock
> contention.
Right. Or more specifically, lock contention while you have VCPU
overcommit.
> our current aim was to have before any printk happens.
> So I 'll trim the comment to somethings like :
>
> Setup pv_lock_ops to exploit KVM_FEATURE_WAIT_FOR_KICK if present.
> This needs to be setup early in boot. ?
You can hook the smp_ops.smp_prepare_cpus call and initialize it there.
There's no need to add new hook code.
J
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