netdev - Re: [PATCH v3 1/6] net: pad skb data and shinfo as a whole rather than individually

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Wed, 25 Jan 2012 13:51:19 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Ian Campbell <ian.campbell@...rix.com>
Cc:	netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH v3 1/6] net: pad skb data and shinfo as a whole rather
 than individually

Le mercredi 25 janvier 2012 à 12:27 +0000, Ian Campbell a écrit :
> This reduces the minimum overhead required for this allocation such that the
> shinfo can be grown in the following patch without overflowing 2048 bytes for a
> 1500 byte frame.
> 
> Reducing this overhead while also growing the shinfo means that sometimes the
> tail end of the data can end up in the same cache line as the beginning of the
> shinfo. Specifically in the case of the 64 byte cache lines on a 64 bit system
> the first 8 bytes of shinfo can overlap the tail cacheline of the data. In many
> cases the allocation slop means that there is no overlap.
> 
> Signed-off-by: Ian Campbell <ian.campbell@...rix.com>
> Cc: "David S. Miller" <davem@...emloft.net>
> Cc: Eric Dumazet <eric.dumazet@...il.com>
> ---

Hmm... you missed build_skb() and all places we use
SKB_DATA_ALIGN(sizeof(struct skb_shared_info))

(for example in some drivers)

If you want to see possible performance impact of your changes, see
commit e52fcb2462ac (bnx2x: uses build_skb() in receive path), and
expect a drop from 820.000 pps to 720.000 pps



--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html