linux-kernel - Re: [RFC][PATCH] srcu: Implement call

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Message-ID: <1328017807.2446.230.camel@twins>
Date:	Tue, 31 Jan 2012 14:50:07 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Avi Kivity <avi@...hat.com>
Cc:	"Paul E. McKenney" <paulmck@...ibm.com>,
	Oleg Nesterov <oleg@...hat.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	KVM list <kvm@...r.kernel.org>
Subject: Re: [RFC][PATCH] srcu: Implement call_srcu()

On Tue, 2012-01-31 at 15:47 +0200, Avi Kivity wrote:

> They really need to return quickly to userspace, and they really need to
> perform some operation between rcu_assign_pointer() and returning, so no.

Bugger :/

> >
> > Compile tested only!! :-)
> >
> 
> How much did synchronize_srcu_expedited() regress?  Presumably your
> compiler didn't tell you that.

Nope, quite a lot I figure.

> Can we get it back to speed by scheduling a work function on all cpus? 
> wouldn't that force a quiescent state and allow call_srcu() to fire?
> 
> In kvm's use case synchronize_srcu_expedited() is usually called when no
> thread is in a critical section, so we don't have to wait for anything
> except the srcu machinery.

OK, I'll try and come up with means of making it go fast again ;-)
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