Date: Tue, 09 Sep 2008 08:02:36 -0700 From: Sam Leffler <sam@freebsd.org> To: Jacques Fourie <jacques.fourie@gmail.com> Cc: freebsd-arm@freebsd.org Subject: Re: Routing benchmarks Message-ID: <48C6900C.8070708@freebsd.org> In-Reply-To: <be2f52430809090736v4ab9c87bu2a0adced13811801@mail.gmail.com> References: <be2f52430809090633o7b80f23y2749a055f61d5cb0@mail.gmail.com> <20080909175556.07bac5f0.stas@FreeBSD.org> <be2f52430809090736v4ab9c87bu2a0adced13811801@mail.gmail.com>
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Jacques Fourie wrote: > On Tue, Sep 9, 2008 at 3:55 PM, Stanislav Sedov <stas@freebsd.org> wrote: > >> On Tue, 9 Sep 2008 15:33:30 +0200 >> "Jacques Fourie" <jacques.fourie@gmail.com> mentioned: >> >> >>> Hi, >>> >>> I've performed some benchmark tests on my Gumstix Connex 400 (Intel >>> Xscale PXA 255 CPU clocked at 400MHz) with a netDuo expansion board. >>> This board has two smc network interfaces. I configure the gumstix as >>> a router and measure network throughput with netperf running on >>> seperate boxes on either side of the gumstix. My initial tests showed >>> a TCP throughput of 2Mbit/s. After adapting the smc driver to use DMA >>> this figure went up to 7Mbit/s. Although this is a significant >>> improvement, it still seems to be a bit slow. Does anyone have any >>> tips on how I can go about to try and figure out where the bottleneck >>> lies? Initial profiling showed that a significant amount of time was >>> spent doing memory to memory copies of data, but after the DMA change >>> profiling does not show any obvious culprits. >>> >>> >> Have you tried checking the speed of the interface itself? Without >> routing involved? May it be the interfaces itself being so slow? >> >> -- >> Stanislav Sedov >> ST4096-RIPE >> >> > > Running netserver on the gumstix shows a throughput of 2.4Mbit/s. At > the moment I can't get if_bridge to work - will try to figure out what > is going on. A bridging benchmark may be more informative. > You said you did profiling but you didn't provide the data to inspect. It's possible kernel profiling has never been tried on your platform; did you sanity check the results? (e.g. run a known test load and check results; verify all routines that should execute appear in the profile). Also if copy overhead shows up as significant look to see why those copies are being done; it's often possible to avoid a copy. My experience in working with architectures like this is that cache handling can be a significant cost that doesn't always show up on a profile. Also you may find useful information by tracking mbufs using the h/w clock at important places along the "fast path" then look at whether the overhead for each step is reasonable. I did this for bridged traffic by forcing the rx dma to go to an mbuf+cluster then used the free storage in the mbuf header to store timestamps. At the end of the processing path I sorted the data into buckets by the sample points and added a sysctl to dump the histogram to see min/max/avg. Sam
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