netdev - Re: [net-next PATCH 4/4] fib_trie: Remove leaf

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Message-ID: <54EE65E9.9010302@gmail.com>
Date:	Wed, 25 Feb 2015 16:16:41 -0800
From:	Alexander Duyck <alexander.duyck@...il.com>
To:	Julian Anastasov <ja@....bg>,
	Alexander Duyck <alexander.h.duyck@...hat.com>
CC:	netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>
Subject: Re: [net-next PATCH 4/4] fib_trie: Remove leaf_info

On 02/25/2015 04:06 PM, Julian Anastasov wrote:
> 	Hello,
>
> On Wed, 25 Feb 2015, Alexander Duyck wrote:
>
>>> 	If there is some fa in list with higher fa_slen
>>> fib_find_alias will always stop the loop and come with
>>> fa != NULL, so above 'if...break' is not needed, we are
>>> always going to add at tail when fa is NULL.
>> Actually fib_find_alias will return NULL in the case that there was a hole in
>> which the suffix length does not exist.
>>
>> So for example if we have a suffix length of 8 and one of 10 and we are adding
>> a suffix length of 9 then fib_find_alias will return NULL and we need to walk
>> though the list and find the hole we are supposed to drop the suffix in.
> 	I missed the fact that we return NULL instead of fa.
> I thought, it would be more consistent with the old logic
> to return a stop position. And we avoid walking the list
> again. But in practice we should not see many entries here,
> right?

Most users should have a pretty shallow list here.  In the case of BGP
routes there might be more entries per slen but the odds of encountering
a NULL in that case should be pretty low.

>> Why are you showing me an example with a 32b int when I am using a long?  For
>> x86 a 32b shift on a 32b value is undefined so we need to compare the suffix
>> length to the KEYLENGTH.  For 64b a long value can be shifted up to 63 bits
>> and still be a defined value.  That is why I use "1ul" as the value being
>> shifted and then also perform the check for KEYLENGTH vs BITS_PER_LONG in
>> order to determine if I still need the check for fa_slen != KEYLENGTH.
> 	I see, so, on 64-bit platform we avoid the
> KEYLENGTH check... OK, that is better.
>
> Regards
>
> --
> Julian Anastasov <ja@....bg>

Yes, the BIT_PER_LONG check will be broken down to either 0 or 1 by the
complier so it will be stripped out in the resulting assembler.

- Alex
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