Date: Mon, 19 Jun 2006 09:19:13 -0400 From: John Baldwin <jhb@freebsd.org> To: Andre Oppermann <andre@freebsd.org> Cc: "Bjoern A. Zeeb" <bzeeb-lists@lists.zabbadoz.net>, src-committers@freebsd.org, cvs-all@freebsd.org, cvs-src@freebsd.org, Sam Leffler <sam@errno.com> Subject: Re: cvs commit: src/sys/netinet tcp_var.h Message-ID: <200606190919.13866.jhb@freebsd.org> In-Reply-To: <449552C9.7060203@freebsd.org> References: <200606171757.k5HHvahf087725@repoman.freebsd.org> <20060618080019.B60374@maildrop.int.zabbadoz.net> <449552C9.7060203@freebsd.org>
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On Sunday 18 June 2006 09:19, Andre Oppermann wrote: > Bjoern A. Zeeb wrote: > > On Sun, 18 Jun 2006, Sam Leffler wrote: > >=20 > >> Andre Oppermann wrote: > >>> andre 2006-06-17 17:57:36 UTC > >>> > >>> FreeBSD src repository > >>> > >>> Modified files: > >>> sys/netinet tcp_var.h > >>> Log: > >>> Rearrange fields in struct syncache and syncache_head to make them= =20 > >>> more > >>> cache line friendly. > >> > >> Got any benchmarks to back this up? Or perhaps it was just the smiley > >> face your cache lines gave you :) >=20 > The entry chains are traversed quite often and the first thing looked > at is in_conninfo and then sc_rxttime and sc_rxmits. So it makes a > lot of sense to have them close together on the same cache line aligned > to the beginning of the struct and to the native alignment of the > architecture. I did not benchmark it but it is simple reasoning. I was talking with Alan Cox at USENIX ATC about working on SMP, and one of the comments he made about doing SMP stuff in the kernel in that what=20 you would intuitively think would be faster doesn't always end up that way in practice. In fact, it sometimes ends up being the opposite of what is intuitive. I agree that you should really benchmark things and not just assume they will make performance better. =2D-=20 John Baldwin <jhb@FreeBSD.org> =A0<>< =A0http://www.FreeBSD.org/~jhb/ "Power Users Use the Power to Serve" =A0=3D =A0http://www.FreeBSD.org
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