linux-kernel - Re: per-cpu operation madness vs validation

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Message-ID: <alpine.DEB.2.00.1107280847270.12379@router.home>
Date:	Thu, 28 Jul 2011 08:50:57 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Thomas Gleixner <tglx@...utronix.de>
cc:	Peter Zijlstra <peterz@...radead.org>, Tejun Heo <tj@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Paul E. McKenney" <paulmck@...ibm.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>, eric.dumazet@...il.com
Subject: Re: per-cpu operation madness vs validation

On Thu, 28 Jul 2011, Thomas Gleixner wrote:

> We just have to understand, that preempt_disable, bh_disable,
> irq_disable are cpu local BKLs with very subtle semantics which are
> pretty close to the original BKL horror. All these mechanisms are per
> cpu locks in fact and we need to get some annotation in place which
> will help understandability and debugability in the first place. The
> side effect that it will help RT to deal with that is - of course
> desired from our side - but not the primary goal of that excercise.

Well the use of the per cpu atomic operations instead of disabling
preemption or scheduling helps RT too by removing the need to do so from
critical OS paths. F.e. we were able to remove most of that from counter
increments. There is still some more work to be done with these
byte/packet counters there as well.

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