linux-kernel - Re: [PATCH RFC V6 0/11] Paravirtualized ticketlocks

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Message-ID: <4F7855A1.80107@redhat.com>
Date:	Sun, 01 Apr 2012 16:18:25 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
CC:	Alan Meadows <alan.meadows@...il.com>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	the arch/x86 maintainers <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	KVM <kvm@...r.kernel.org>, Andi Kleen <andi@...stfloor.org>,
	Xen Devel <xen-devel@...ts.xensource.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Virtualization <virtualization@...ts.linux-foundation.org>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
	Stephan Diestelhorst <stephan.diestelhorst@....com>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	Attilio Rao <attilio.rao@...rix.com>
Subject: Re: [PATCH RFC V6 0/11] Paravirtualized ticketlocks

On 03/30/2012 01:07 PM, Raghavendra K T wrote:
> On 03/29/2012 11:33 PM, Raghavendra K T wrote:
>> On 03/29/2012 03:28 PM, Avi Kivity wrote:
>>> On 03/28/2012 08:21 PM, Raghavendra K T wrote:
>
>> I really like below ideas. Thanks for that!.
>>
>>> - from the PLE handler, don't wake up a vcpu that is sleeping
>>> because it
>>> is waiting for a kick
>>
>> How about, adding another pass in the beginning of kvm_vcpu_on_spin()
>> to check if any vcpu is already kicked. This would almost result in
>> yield_to(kicked_vcpu). IMO this is also worth trying.
>>
>> will try above ideas soon.
>>
>
> I have patch something like below in mind to try:
>
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index d3b98b1..5127668 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -1608,15 +1608,18 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me)
>       * else and called schedule in __vcpu_run.  Hopefully that
>       * VCPU is holding the lock that we need and will release it.
>       * We approximate round-robin by starting at the last boosted VCPU.
> +     * Priority is given to vcpu that are unhalted.
>       */
> -    for (pass = 0; pass < 2 && !yielded; pass++) {
> +    for (pass = 0; pass < 3 && !yielded; pass++) {
>          kvm_for_each_vcpu(i, vcpu, kvm) {
>              struct task_struct *task = NULL;
>              struct pid *pid;
> -            if (!pass && i < last_boosted_vcpu) {
> +            if (!pass && !vcpu->pv_unhalted)
> +                continue;
> +            else if (pass == 1 && i < last_boosted_vcpu) {
>                  i = last_boosted_vcpu;
>                  continue;
> -            } else if (pass && i > last_boosted_vcpu)
> +            } else if (pass == 2 && i > last_boosted_vcpu)
>                  break;
>              if (vcpu == me)
>                  continue;
>

Actually I think this is unneeded.  The loops tries to find vcpus that
are runnable but not running (vcpu_active(vcpu->wq)), and halted vcpus
don't match this condition.

-- 
error compiling committee.c: too many arguments to function

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