linux-kernel - Re: Inline local_bh_disable when TRACE

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Date:	Wed, 19 Dec 2007 15:03:13 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: Inline local_bh_disable when TRACE_IRQFLAGS

* Herbert Xu <herbert@...dor.apana.org.au> wrote:

> On Wed, Dec 19, 2007 at 12:31:52PM +0100, Ingo Molnar wrote:
> >
> > > So I'm wondering if it would be reasonable to make it out-of-line 
> > > when TRACE_IRQFLAGS is off.  This may make a difference because 
> > > the networking stack is a frequent user of local_bh_disable and 
> > > local_bh_enable.
> > 
> > do you mean to make it inline again?
> 
> Yes I meant in-line :)

if that decreases code size then i guess we could do that.

> > (btw., generally i think local_bh_disable() is a poor API because it 
> > is opaque about the data structure dependency that it governs. 
> > Explicit exclusion rules generally work better.)
> 
> I see where you're coming from especially with your preemptible 
> softirq work.  However I'm mostly thinking about the existing callers 
> of local_bh_disable in the networking stack.

yeah, i was just commenting on the general concept of 'naked' 
local_bh_disable(). And just to make it clear: with that i'm not 
implying anything about the quality of the networking code - networking 
is one of the cleanest [if not the cleanest] subsystems in the kernel. 

It's just that it's long term more useful for us if our "global scope" 
APIs have direct, programmatic relationship to the data structures / 
data flow they control. So i'd love to have the same flow/performance, 
just coded a bit more explicitly. [preempt_disable() for example has 
similar issues.]

	Ingo
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