Re: [Qemu-devel] [PATCH] [RFC] Convert Qemu Timer List and Active Timers to RCU

[Mike Day]

On Thu, Feb 13, 2014 at 4:25 AM, Paolo Bonzini <address@hidden> wrote:
> Il 13/02/2014 10:11, Alex Bligh ha scritto:
>>
>> I'll certainly have a look through this. However before I do, what
>> problem is this trying to solve? Do we think there is possibility
>> of contention on the active timers lock? I used to think this was
>> taken (let alone contented) relatively infrequently, but Rob Herring's
>> recent email suggests to me the list is being modified in some
>> circumstances rather more frequently than I thought.
>
> I think that, more than contention, it tries to reduce the cost of
> synchronization primitives, especially the locking and unlocking of the list
> around the invocation of timer callbacks.

Yes, the assumption is that the active timers are a read-mostly list,
so rcu is a win.

Mike