linux-kernel - Re: [PATCH v2 tip/core/rcu 0/13] Miscellaneous fixes for 4.12

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Message-Id: <20170419130245.GJ3956@linux.vnet.ibm.com>
Date:   Wed, 19 Apr 2017 06:02:45 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, mingo@...nel.org,
        jiangshanlai@...il.com, dipankar@...ibm.com,
        akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
        josh@...htriplett.org, tglx@...utronix.de, rostedt@...dmis.org,
        dhowells@...hat.com, edumazet@...gle.com, dvhart@...ux.intel.com,
        fweisbec@...il.com, oleg@...hat.com, bobby.prani@...il.com,
        marc.zyngier@....com
Subject: Re: [PATCH v2 tip/core/rcu 0/13] Miscellaneous fixes for 4.12

On Wed, Apr 19, 2017 at 01:28:45PM +0200, Peter Zijlstra wrote:
> 
> So the thing Maz complained about is because KVM assumes
> synchronize_srcu() is 'free' when there is no srcu_read_lock() activity.
> This series 'breaks' that.
> 
> I've not looked hard enough at the new SRCU to see if its possible to
> re-instate that feature.

And with the fix I gave Maz, the parallelized version is near enough
to being free as well.  It was just a stupid bug on my part: I forgot
to check for expedited when scheduling callbacks.

							Thanx, Paul