netdev - Re: xfrm_state locking regression...

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Message-ID: <20080923045951.GA26048@gondor.apana.org.au>
Date:	Tue, 23 Sep 2008 12:59:51 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Timo Teräs <timo.teras@....fi>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: xfrm_state locking regression...

On Tue, Sep 23, 2008 at 07:53:18AM +0300, Timo Teräs wrote:
>
> So the idea was to hold X->next from deletion function, not from
> the walking function. That would be, we always hold deleted->next when
> there are ongoing walks. And on final _put() we _put() the ->next
> entry.
> 
> I think that would work.

Right, this would work.

However, now you're again slowing down the relatively fast path of
state deletion by moving extra work there from the non-critical
dump path.

When we optimise code for time, we don't necessarily try to minimise
the work overall.  We instead try to minimise the amount of work on
the critical paths.  It's OK to let the other paths such as dumping
do a bit more work if it improves the fast paths.

Cheers,
-- 
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Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au>
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