netdev - Re: [PATCH v2 net-next] tcp: md5: use kmalloc() backed scratch areas

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Message-ID: <20160629153818.GA29838@gondor.apana.org.au>
Date:	Wed, 29 Jun 2016 23:38:18 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	David Miller <davem@...emloft.net>,
	Network Development <netdev@...r.kernel.org>
Subject: Re: [PATCH v2 net-next] tcp: md5: use kmalloc() backed scratch areas

On Wed, Jun 29, 2016 at 08:26:43AM -0700, Andy Lutomirski wrote:
> 
> Two reasons:
> 
> 1. Code like tcp md5 would be simpler if it could pass a scatterlist
> to hash the skb but use a virtual address for the header.

True.  But I bet we can make it simpler in other ways without
creating special interfaces for it.  Look at how we do IPsec
encryption/hashing, this is what TCP md5 should look like.  But
nobody in their right mind would bother doing this because this
is dead code.

> 2. The actual calling sequence and the amount of indirection is much
> less for shash, so hashing short buffer is probably *much* faster.

Really?

Have you measured the speed difference between the ahash and shash
interfaces? Are you sure that this would matter when compared
against the speed of hashing a single MD5 block?

Cheers,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt