netdev - Re: [net-next PATCH] ipv4: FIB Local/MAIN table collapse

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Date:	Wed, 11 Mar 2015 09:03:07 -0700
From:	Dave Taht <dave.taht@...il.com>
To:	Alexander Duyck <alexander.duyck@...il.com>
Cc:	Alexander Duyck <alexander.h.duyck@...hat.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Stephen Hemminger <stephen@...workplumber.org>,
	Jiří Pírko <jiri@...nulli.us>,
	Scott Feldman <sfeldma@...il.com>,
	"davem@...emloft.net" <davem@...emloft.net>,
	Sabrina Dubroca <sd@...asysnail.net>
Subject: Re: [net-next PATCH] ipv4: FIB Local/MAIN table collapse

On Wed, Mar 11, 2015 at 7:58 AM, Alexander Duyck
<alexander.duyck@...il.com> wrote:
> On 03/06/2015 01:47 PM, Alexander Duyck wrote:
>> This patch is meant to collapse local and main into one by converting
>> tb_data from an array to a pointer.  Doing this allows us to point the
>> local table into the main while maintaining the same variables in the
>> table.
>>
>> As such the tb_data was converted from an array to a pointer, and a new
>> array called data is added in order to still provide an object for tb_data
>> to point to.
>>
>> In order to track the origin of the fib aliases a tb_id value was added in
>> a hole that existed on 64b systems.  Using this we can also reverse the
>> merge in the event that custom FIB rules are enabled.
>>
>> With this patch I am seeing an improvement of 20ns to 30ns for routing
>> lookups as long as custom rules are not enabled, with custom rules enabled
>> we fall back to split tables and the original behavior.
>>
>> Signed-off-by: Alexander Duyck <alexander.h.duyck@...hat.com>
>> ---
>>
>> Changes since the RFC:
>>   Added tb_id value so I could split main and local for custom rules
>>   Added functionality to split tables if custom rules were enabled
>>   Added table replacement and unmerge functions
>>
>> I have done some testing on this to verify performance gains and that I can
>> split the tables correctly when I enable custom rules, but this patch is
>> what I would consider to be high risk since I am certain there are things I
>> have not considered.
>>
>> If this gets pulled into someone's switchdev tree instead of into net-next I
>> would be perfectly fine with that as I am sure this can use some additional
>> testing.
>
> Has anyone out there had a chance to review this patch?  I had suggested
> holding off on applying it to net-next for additional testing, but I
> haven't found anything, and the only related issue is the one issue
> Sabrina reported for the RTNL locking which was already in net-next anyway.


My environment consists largely of 32 bit routing platforms (openwrt)
running the current homenet routing protocol (babel), using, in
particular, the babeld source specific routing extensions ( see
http://arxiv.org/pdf/1403.0445v3.pdf  ) which do use multiple routing
tables, and other uncommon things like p2p routes and odd netmasks
like /27 and /30.

But: I simply can't keep up with you and this entire patchset changes
so dramatically how routing works that you make me nervous. I would
like to see quagga (and babeld) improved to use atomic updates in
particular (They do a delete + add for no good reason), and for
protocols like ospf, bgp, etc, to be actively tested on real traffic
loads on live data against this entire patchset.

Your 64 bit x86 benchmarks are very exciting and I do look forward to
one day soon attempting to evaluate and benchmark these changes on
teeny 32 bit platforms both in the general case and in this
environment, and am mostly just hoping that others that are doing
higher end real world routing with big tables (such as BGP) are paying
more attention than I can.

What test procedures are you using at present (and what is everyone else using)?

> If nobody has any objections then maybe we should apply this after
> Sabrina's patch and see what other bugs if any can be found when this
> goes into linux-next?  I figure that since the performance gains from
> this patch are fairly significant the risk is likely worth the reward.
>
> - Alex
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-- 
Dave Täht
Let's make wifi fast, less jittery and reliable again!

https://plus.google.com/u/0/107942175615993706558/posts/TVX3o84jjmb
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