Inline local_bh_disable when TRACE_IRQFLAGS

Inline local_bh_disable when TRACE_IRQFLAGS

[Herbert Xu]

Hi Ingo:

I noticed that local_bh_disable is now always out-of-line.  The
change was made when TRACE_IRQFLAGS was added.  However, with
TRACE_IRQFLAGS off, local_bh_disable does exactly the same work
as before.  In particular, it does pretty much the same as what
preempt_disable does and the latter is always inline.

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.

Thanks,
-- 
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Email: Herbert Xu ~{PmV>HI~} <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
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Re: Inline local_bh_disable when TRACE_IRQFLAGS

[Ingo Molnar]

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

> Hi Ingo:
> 
> I noticed that local_bh_disable is now always out-of-line.  The change 
> was made when TRACE_IRQFLAGS was added.  However, with TRACE_IRQFLAGS 
> off, local_bh_disable does exactly the same work as before.  In 
> particular, it does pretty much the same as what preempt_disable does 
> and the latter is always inline.
> 
> 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?

(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.)

	Ingo

Re: Inline local_bh_disable when TRACE_IRQFLAGS

[Herbert Xu]

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 :)

> (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.

Thanks,
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

Re: Inline local_bh_disable when TRACE_IRQFLAGS

[Ingo Molnar]

* Herbert Xu <herbert@gondor.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