netdev - Re: [PATCH v4 1/2] core: Factor out flow calculation from get_rps

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Message-ID: <AANLkTikURsh5wSdOE0_qXDw=XgNMSp5CJ1RytQnBvoyD@mail.gmail.com>
Date:	Wed, 4 Aug 2010 21:38:39 +0800
From:	Changli Gao <xiaosuo@...il.com>
To:	Krishna Kumar2 <krkumar2@...ibm.com>
Cc:	arnd@...db.de, bhutchings@...arflare.com, davem@...emloft.net,
	mst@...hat.com, netdev@...r.kernel.org, therbert@...gle.com
Subject: Re: [PATCH v4 1/2] core: Factor out flow calculation from get_rps_cpu

On Wed, Aug 4, 2010 at 8:02 PM, Krishna Kumar2 <krkumar2@...ibm.com> wrote:
> Changli Gao <xiaosuo@...il.com> wrote on 08/04/2010 04:52:58 PM:
>>
>> the return value of skb_get_rxhash() maybe skb->rxhash, so we don't
>> need to assign it to skb->rxhash again. Use a local variable to save
>> the value and __skb_get_rxhash() should cache the rxhash into
>> skb->rxhash for future use.
>
> I wanted the function to return a rxhash instead of save+return,
> since other users, eg macvtap, doesn't need the rxhash beyond
> calculating a rxq with that hash. So for those users, we can
> avoid updating both skb->rxhash and a local variable (since with
> your suggestion, rps will update either one or two variables
> depending on whether rxhash is cached or not). I am not sure
> which is better.
>

rxhash can also be generated by NIC(hardware) and used some where
else. So for these users, generating the rxhash again is wasting time.
Thanks.


-- 
Regards,
Changli Gao(xiaosuo@...il.com)
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