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RE: [Xen-devel] Ticket spinlocks and MP guests

To: "Keir Fraser" <Keir.Fraser@xxxxxxxxxxxx>, "Espen Skoglund" <espen.skoglund@xxxxxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: RE: [Xen-devel] Ticket spinlocks and MP guests
From: "Tian, Kevin" <kevin.tian@xxxxxxxxx>
Date: Fri, 15 Feb 2008 09:03:49 +0800
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Thread-index: AchvHZx52xVv2tsQEdyZRwAWy6hiGQAUAqPw
Thread-topic: [Xen-devel] Ticket spinlocks and MP guests
>From: Keir Fraser
>Sent: 2008年2月14日 23:24
>On 14/2/08 13:43, "Espen Skoglund" 
><espen.skoglund@xxxxxxxxxxxxx> wrote:
>> Do people feel that the new ticket spinlocks should raise any
>> concerns, or do typical Xen SMP guest workloads remain largely
>> unaffected by the new locking scheme?
>That's a good question which I do not think can be answered 
>without taking
>some measurements. If it's an issue we might consider pv_ops'ifying
>spinlocks to turn them into sleeping locks (this would be easy 
>these days,
>since spin_lock() and spin_unlock() are not inlined). I have 
>some neat ideas
>about how that might work requiring no extra space for 
>spinlock_t and no
>modifications at the hypervisor interface.
>I suppose it depends whether there are any hot spinlocks in 
>the kernel these
>days. I know things have improved a lot in recent years with 
>things like
>RCU. Most spinlock regions are now pretty short.

The side effect is to enlarge average critical section length, if 
most spinlock regions are pretty short.


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