Date: Tue, 9 Sep 2008 17:16:31 +0200 From: "Jacques Fourie" <jacques.fourie@gmail.com> To: "Sam Leffler" <sam@freebsd.org> Cc: freebsd-arm@freebsd.org Subject: Re: Routing benchmarks Message-ID: <be2f52430809090816v57c2c80u6a48446b1e875361@mail.gmail.com> In-Reply-To: <48C6900C.8070708@freebsd.org> References: <be2f52430809090633o7b80f23y2749a055f61d5cb0@mail.gmail.com> <20080909175556.07bac5f0.stas@FreeBSD.org> <be2f52430809090736v4ab9c87bu2a0adced13811801@mail.gmail.com> <48C6900C.8070708@freebsd.org>
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On Tue, Sep 9, 2008 at 5:02 PM, Sam Leffler <sam@freebsd.org> wrote: > 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 > > Thanks for the nice idea - will try something similar. At the moment I'm also suspecting that cache handling has got a lot to do with the performance figures that I'm seeing. The PXA255 has a 32KB data and 32KB instruction cache. Jacques
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