Date: Thu, 20 May 2010 02:05:05 +0700 From: Eugene Grosbein <eugen@grosbein.pp.ru> To: rihad <rihad@mail.ru> Cc: freebsd-net@freebsd.org Subject: Re: increasing em(4) buffer sizes Message-ID: <20100519190505.GA29133@rdtc.ru> In-Reply-To: <4BF4252F.8000208@mail.ru> References: <4BF4252F.8000208@mail.ru>
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On Wed, May 19, 2010 at 10:51:43PM +0500, rihad wrote: > We have a FreeBSD 7.2 Intel Server System 4GB RAM box doing traffic > shaping and accounting. It has two em gigabit interfaces: one used for > input, the other for output, servicing around 500-600 mbps load through > it. Traffic limiting is accomplished by dynamically setting up IPFW > pipes, which in turn work fine for our per-user traffic accounting needs > thanks to byte counters. So the firewall is basically a longish string > of pipe rules. This worked fine when the number of online users was low, > but now, as we've slowly begun servicing 2-3K online users netstat -i's > Ierrs column is growing at a rate of 5-15K per hour for em0, the > interface used for input. Apparently searching through the firewall > linearly for _each_ arriving packet locks the interface for the duration > of the search (even though net.isr.direct=0), so some packets are > periodically dropped on input. To mitigate the problem I've set up a > two-level hash by means of skipto rules, dropping the number of up to > several thousand rules to be searched for each packet to a mere 85 max, > but the rate of Ierrs has only increased to 40-50K per hour, I don't > know why. I've also tried setting these sysctls: First, read: http://www.intel.com/design/network/applnots/ap450.htm You'll see you may be restricted with your NIC's chip capabilities. > hw.intr_storm_threshold=10000 > dev.em.0.rx_processing_limit=3000 > > but they didn't help at all. BTW, the other current settings are: > kern.hz=4000 > net.inet.ip.fw.verbose=0 > kern.ipc.nmbclusters=111111 > net.inet.ip.fastforwarding=1 > net.inet.ip.dummynet.io_fast=1 > net.isr.direct=0 > net.inet.ip.intr_queue_maxlen=5000 > > net.inet.ip.intr_queue_drops is always zero. > > I think the problem lies in the buffer size of em not being large enough > to buffer the packets as they're arriving. I looked in > /sys/dev/e1000/if_em.c and found this: > > in em_attach(): > adapter->rx_buffer_len = 2048; > > and later in em_initialize_receive_unit(): > switch (adapter->rx_buffer_len) { > default: > case 2048: > rctl |= E1000_RCTL_SZ_2048; > break; > case 4096: > rctl |= E1000_RCTL_SZ_4096 | > E1000_RCTL_BSEX | E1000_RCTL_LPE; > break; > case 8192: > rctl |= E1000_RCTL_SZ_8192 | > E1000_RCTL_BSEX | E1000_RCTL_LPE; > break; > case 16384: > rctl |= E1000_RCTL_SZ_16384 | > E1000_RCTL_BSEX | E1000_RCTL_LPE; > break; > } > > > So apparently the default buffer size is 2048 bytes, and as much as > 16384 is supported. But at what price? Those constants do look > suspicious. Can I blindly change rx_buffer_len in em_attach()? Sorry, > I'm not a kernel hacker :( There are loader tunnables, set them in /etc/loader.conf: hw.em.rxd=4096 hw.em.txd=4096 The price is amount of kernel memory the driver may consume. Maxumum MTU=16110 for em(4), so it can consume about 64Mb of kernel memory for that long input buffer, in theory. Some more useful tunnables for loader.conf: dev.em.0.rx_int_delay=200 dev.em.0.tx_int_delay=200 dev.em.0.rx_abs_int_delay=200 dev.em.0.tx_abs_int_delay=200 dev.em.0.rx_processing_limit=-1 Alternatively, you may try kernel polling (ifconfig em0 polling) with other tunnables: kern.hz=4000 # for /boot/loader.conf kern.polling.burst_max=1000 # for /etc/sysctl.conf kern.polling.each_burst=500 Eugene Grosbein
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