netdev - RE: [PATCH 6/7] mlx4_en: Adding rxhash support

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Date:	Tue, 18 Oct 2011 07:36:21 +0000
From:	Yevgeny Petrilin <yevgenyp@...lanox.co.il>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	"davem@...emloft.net" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: [PATCH 6/7] mlx4_en: Adding rxhash support

> >  	rss_context->flags = rss_mask;
> > +	rss_context->hash_fn = 1;
> > +	for (i = 0; i < 10; i++)
> > +		rss_context->rss_key[i] = random32();
> >
> 
> Thats bit of a problem : Two NICS will have different seeds, and thus provide different rxhash for a given flow. A bonding of two NICS will
> not be able to provide a consistent rxhash.
> 
> drivers/net/ethernet/intel/igb/igb_main.c uses a static table to avoid this problem.
> 

Hello Eric, thanks for your review.

I agree that in this case two ports will have different seeds.
But even if we use static values for the key, what about bonding of 2 NICs from different vendors?
How can we ensure we get same rxhash value for all NICs?

There are also other drivers that use random values as well, for example:
drivers/net/ethernet/broadcom/bnx2x/bnx2x_cmn.c

Thanks,
Yevgeny