Date: Wed, 3 Aug 2005 12:23:19 +0300 From: Victor Semionov <victor@vmpbg.com> To: Chuck Swiger <cswiger@mac.com>, freebsd-questions@freebsd.org Subject: Re: polling decreases throughput ~50% Message-ID: <200508031223.20065.victor@vmpbg.com> In-Reply-To: <42EFBF4A.2010209@mac.com> References: <200508021537.26986.victor@vmpbg.com> <20050802173421.GA34971@alexis.mi.celestial.com> <42EFBF4A.2010209@mac.com>
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> >> Why is that? I thought polling should decrease CPU usage by avoiding too > >> many context switches when a hw irq is generated frequently, but it > >> shouldn't make the transfer slower if there are no other jobs running. > > You have to poll often enough to keep the pipe full, otherwise your max > throughput can be limited. Also, rl hardware isn't the greatest and > probably requires a lot more CPU than a device with working buffer/DMA > design. HZ is 1000, which I guess should be more than enough with kern.polling.burst_max=150. Indeed, it was hardware's fault - my other NIC is a fxp and I got much better results with it - less CPU, while throughput stayed the same as without polling.
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