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Date: Sat, 31 Mar 2012 09:39:15 +0530
From: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>,
        Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>,
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Subject: Re: [PATCH RFC V6 0/11] Paravirtualized ticketlocks
Message-ID: <20120331040915.GF13345@linux.vnet.ibm.com>
Reply-To: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
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* Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com> [2012-03-31 09:37:45]:

> The issue is with ticketlocks though. VCPUs could go into a spin w/o
> a lock being held by anybody. Say VCPUs 1-99 try to grab a lock in
> that order (on a host with one cpu). VCPU1 wins (after VCPU0 releases it)
> and releases the lock. VCPU1 is next eligible to take the lock. If 

Sorry I meant to say "VCPU2 is next eligible ..."

> that is not scheduled early enough by host, then remaining vcpus would keep 
> spinning (even though lock is technically not held by anybody) w/o making 
> forward progress.
> 
> In that situation, what we really need is for the guest to hint to host
> scheduler to schedule VCPU1 early (via yield_to or something similar). 

s/VCPU1/VCPU2 ..

- vatsa