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Re: [Xen-devel] rcu support in xen

To: <ncmike@xxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] rcu support in xen
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Sun, 25 Mar 2007 09:28:30 +0100
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On 24/3/07 19:22, "Mike D. Day" <ncmike@xxxxxxxxxx> wrote:

> Due to recent conversion of get_domain_by_id to use rcu techniques I
> looked at the file xen/include/xen/rcupdate.h and noticed
> rcu_read_lock is defined as:
> define rcu_read_lock(x)       do { } while (0)
> as well as the corresponding unlock and other related macros.
> Apologies if this has already been answered, but when will the real
> rcu code get into -unstable?

The whole point of RCU is that read-side critical sections have no (or very
little) synchronisation overhead. In Xen the rcu_read_[un]lock functions are
only present to make the code clearer and to seome extent self documenting.
On Linux they also disable involuntary preemption during the critical
section (which is not needed on Xen, of course).

So, in short, Xen already has a complete RCU implementation.

 -- Keir

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