netdev - Re: [PATCH 1/2] napi_synchronize: waiting for NAPI

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Date:	Wed, 17 Oct 2007 18:26:28 -0700
From:	Stephen Hemminger <shemminger@...ux-foundation.org>
To:	benh@...nel.crashing.org
Cc:	"David S. Miller" <davem@...emloft.net>,
	Jeff Garzik <jgarzik@...ox.com>, netdev@...r.kernel.org
Subject: Re: [PATCH 1/2] napi_synchronize: waiting for NAPI

On Thu, 18 Oct 2007 10:28:09 +1000
Benjamin Herrenschmidt <benh@...nel.crashing.org> wrote:

> 
> On Wed, 2007-10-17 at 13:26 -0700, Stephen Hemminger wrote:
> > plain text document attachment (napi-synchronize.patch)
> > Some drivers with shared NAPI need a synchronization barrier.
> > Also suggested by Benjamin Herrenschmidt for EMAC.
> > 
> > Signed-off-by: Stephen Hemminger <shemminger@...ux-foundation.org>
> 
> Just saw this patch, sorry, missed it. Same as you sent me on another
> reply, I still think it needs the smp barrier. Can you have a look at
> the one I posted today ?
> 
> Cheers,
> Ben.

Could you give a concrete example as to why it needs a smp barrier?
The test_bit is going to get a consistent result. Are you worried about
operations ordering before the test_bit()? In that case, one of those
smp_mb__before_xxx functions is probably what is needed.


-- 
Stephen Hemminger <shemminger@...ux-foundation.org>
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