netdev - Re: [PATCH 00/16] Remove the ipv4 routing cache

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Date:	Fri, 27 Jul 2012 12:06:47 -0700
From:	Alexander Duyck <alexander.duyck@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH 00/16] Remove the ipv4 routing cache

On Fri, Jul 27, 2012 at 9:28 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Fri, 2012-07-27 at 09:23 -0700, Eric W. Biederman wrote:
>
>> I am familiar.  But does hardware prefetching make a difference
>> if your object is less than 64 bytes?
>>
>
> Apparently yes, if the prefetch touches a dirtied neighbour cache line.
>
>> I don't believe only allocating 64 bytes will be a problem,
>> as no one else well be dirtying your cache line.
>>
>> I suppose you could run into pathologies where your object
>> is 3*64 bytes in size, but your expression doesn't handle
>> that case either.
>>
>
> Sure, but in most cases fib objects are under 128 bytes.
>
>
>> The other alternative to guarantee very good cache behavior is
>> to ensure you are allocating a power of two size up to some limit,
>> perhaps page size.
>>
>
> Good idea.
>
>> My point is the magic 128 likely requires an explicatory comment and I
>> think the net result is you have encoded something fragile that is good
>> for testing but that will in the fullness of time do strange things that
>> will be easy to overlook.
>
> Sure, I'll send a v2, thanks.
>
>

I tested out v1 of your patch and didn't seem much of a change in my
test environment.  I figure I will spend most of today going through
the code trying to figure out what is causing the issues I am seeing
and why your changes had no effect on my setup.

Thanks,

Alex
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