netdev - Re: [PATCH net-2.6.26] fib_trie: RCU optimizations

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] [day] [month] [year] [list]

Message-Id: <20080321.154933.81125723.davem@davemloft.net>
Date:	Fri, 21 Mar 2008 15:49:33 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	dada1@...mosbay.com
Cc:	shemminger@...tta.com, paulmck@...ux.vnet.ibm.com,
	netdev@...r.kernel.org
Subject: Re: [PATCH net-2.6.26] fib_trie: RCU optimizations

From: Eric Dumazet <dada1@...mosbay.com>
Date: Fri, 21 Mar 2008 18:44:33 +0100

> Loop is so small that prefetches hints are throwed away by CPU, or the 
> cost to setup the prefetch(register + offset) is too expensive...

That's been my experience as well.

For this reason I consider the unconditional prefetches in the
linux/list.h list iteration macros troublesome.

Most loops are small so by default those macros should not prefetch,
and when you know you have a large enough loop (and thus enough work
to make the prefetch actually matter) you use a specific specially
named variant of the list traversal macro.

Oh yes, and you have to provide performance improvement proof before
submitting a patch that uses the prefetch-using list macro variants.
:-)

--
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