netdev - Re: [RFC] skb align patch

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:	Mon, 21 Sep 2009 08:13:20 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Stephen Hemminger <shemminger@...tta.com>
CC:	Jesse Brandeburg <jesse.brandeburg@...il.com>,
	Jesper Dangaard Brouer <hawk@...u.dk>, netdev@...r.kernel.org
Subject: Re: [RFC] skb align patch

Stephen Hemminger a écrit :
> Based on the Intel suggestion that PCI-express overhead is
> a significant cost.
> 
> Would people doing performance please measure the impact of
> changing SKB alignment (64 bit only).

I had this idea some time ago when I hit a limit on bnx2 adapter
(Giga bit link, BCM5708S), with small packets. pktgen was able
to send ~500 Mbps 'only', or 700kps if I remember well.
So I tried to align the pktgen build packet to a cache line,
it gave no difference at all, but it was on a 32 bit kernel.
(Thus my patch was for pktgen only, not a generic one as yours)

Could you elaborate why this change could be useful on 64bit ?

Thanks

> 
> 
> --- a/arch/x86/include/asm/system.h	2009-09-20 14:08:40.922346912 -0700
> +++ b/arch/x86/include/asm/system.h	2009-09-20 14:14:37.012371200 -0700
> @@ -455,4 +455,14 @@ static inline void rdtsc_barrier(void)
>  	alternative(ASM_NOP3, "lfence", X86_FEATURE_LFENCE_RDTSC);
>  }
>  
> +#ifndef CONFIG_X86_32
> +/*
> + * DMA to unaligned address is more expensive than the the
> + * overhead of unaligned CPU access.
> + */
> +#define NET_IP_ALIGN	0
> +#define NET_SKB_PAD	L1_CACHE_BYTES
> +#endif
> +
> +
>  #endif /* _ASM_X86_SYSTEM_H */
> --

--
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