Date: Thu, 9 Jun 2011 09:11:51 -0400 From: John Baldwin <jhb@freebsd.org> To: freebsd-current@freebsd.org Cc: Luigi Rizzo <rizzo@iet.unipi.it> Subject: Re: any place to look at for PCI-express performance issues ? Message-ID: <201106090911.51817.jhb@freebsd.org> In-Reply-To: <20110609035952.GA30464@onelab2.iet.unipi.it> References: <20110609035952.GA30464@onelab2.iet.unipi.it>
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On Wednesday, June 08, 2011 11:59:52 pm Luigi Rizzo wrote: > hi, > during my tests with netmap with 10Gbit cards (82599, dual port), > i notice that a motherboard with an AMD 880G chipset > is performing significantly worse than an intel based one. > In both cases the NIC is mounted on a 16x PCIe slot, > and in both cases the driver reports the use 5Gb/4x per port. > > On the intel i reach easily 14.88Mpps, on the AMD the card tops > at 1.8Mpps, and is not CPU limited (changing dev.cpu.0.freq does not change > the throughput). > Disabling flow control does not help (and in any case > the other end of the link is the same), and since > I am using the same picobsd image (based on FreeBSD/i386 > head w/ my netmap code) i suspect that the difference in > performance has to do with the PCIe controller. > My netmap code > http://info.iet.unipi.it/~luigi/netmap/ > does nothing special on the bus. > > Now, the question is, is there any place in FreeBSD sources that > might be related to PCIe performance, e.g. initialising specific > features in one or another northbridge, etc ? No, in general we rely on the firmware (BIOS, etc.) to configure those bits. You might take a gander at comparing 'pciconf -lc' output as that displays a few of the PCI-e settings such as the actual number of lanes used, etc. -- John Baldwin
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