netdev - Re: [PATCH net/for-next V1 1/1] IB/ipoib: break linkage to neighbouring system

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Date:	Thu, 19 Jul 2012 19:20:41 +0300
From:	Or Gerlitz <ogerlitz@...lanox.com>
To:	Christoph Lameter <cl@...ux.com>
CC:	Shlomo Pongartz <shlomop@...lanox.com>, <roland@...nel.org>,
	<davem@...emloft.net>, <linux-rdma@...r.kernel.org>,
	<erezsh@...lanox.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH net/for-next V1 1/1] IB/ipoib: break linkage to neighbouring
 system

On 7/19/2012 6:24 PM, Christoph Lameter wrote:
> On Thu, 19 Jul 2012, Shlomo Pongartz wrote:
>
>> The garbage collection and stale times follow the default ipv4/6 neigh.default.gc_yyy
>> sysctl values, for example
>>
>> net.ipv4.neigh.default.gc_interval = 30
>> net.ipv4.neigh.default.gc_stale_time = 60
>>
>> If given access to these values from IPoIB, we will be happy
>> to integrate them into that logic
>
> It looks like the values are hardcoded right now.

Two points here,

1s, they are indeed hard-coded since there's no define/enum
that holds their default values (or maybe we should add one now?), see
this code snippest from net/ipv4/arp.c

>         .gc_interval    = 30 * HZ,
>         .gc_thresh1     = 128,
>         .gc_thresh2     = 512,
>         .gc_thresh3     = 1024,

2nd, and even more interesting, the little challenge here is how
to integrate with the sysctl's that allow for changing these values,
the mechanism that uses neigh_sysctl_table in net/core/neighbour.c isn't
exported to the rest of the world. And there's no point to define new
sysctl entries just for managing the IPoIB neighbours, ideas welcome.


>> Please clarify what do you mean by group expiration.
>
> If you have neighbor expiration periods of 4 hrs and it is necessary to
> run the expiration logic then please expire all the neighbor entries due a
> certain period after that as well to avoid running the expiration again in
> the next minute or so.


This is still a bit unclear here... do you mean to say that at a certain 
point in time,
**all** entries need to be deleted irrelevant of their (jiffies) age? why?

> I guess the fuzz factor needs to scale depending on the expiration period.
>
>

and this is what happens now, the factor is 0.5, entry would be deleted when
if  (60m <= unused < 90s) holds

Or.
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