Date: Wed, 21 Mar 2001 22:20:01 +0100 (MET) From: Helge Oldach <Helge.Oldach@de.origin-it.com> To: conrad@th.physik.uni-bonn.de (Jan Conrad) Cc: bright@wintelcom.net, dillon@earth.backplane.com, gordont@bluemtn.net, rdm@cfcl.com, freebsd-stable@FreeBSD.ORG Subject: Re: NFS performance Message-ID: <200103212120.WAA03934@galaxy.de.cp.philips.com> In-Reply-To: <Pine.BSF.4.33.0103212133210.559-100000@merlin.th.physik.uni-bonn.de> from Jan Conrad at "Mar 21, 2001 9:45:26 pm"
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Jan Conrad: >> >client: >> >Name Mtu Network Address Ipkts Ierrs Opkts Oerrs Coll >> >fxp0 1500 <Link#1> 00:02:b3:1f:f8:c5 1901001 0 771611 0 208240 >> >server: >> >Name Mtu Network Address Ipkts Ierrs Opkts Oerrs Coll >> >fxp0 1500 <Link#1> 00:90:27:1c:f3:79 7157753 0 4648694 0 2661459 >> >> Gimme a break. Out of 4648694 output packets you see as many as 2661459 >> collisions? That's more than 50%, i.e. for about every second packet >> that you are sending you get a collision! You very clearly have a >> collision problem. >> >> I bet that the switch is at full-duplex while you're at half. Try >> changing the mediaopt setting of your NIC. >- if I leave it at half-duplex the net makes 9Mb/s > ping -f <Machine on the same switch) I get 0% to 1% packet loss Excellent. >- if I switch the fxp0 interface to full duplex > and boot the machine and disconnect the net for some seconds > the net slows down to 200kb/s Ooops! >I would conclude that the switch is on 100baseTX, half-duplex, indeed. Yep, most certainly it is. And it's even too stupid to see that you are different. But OK. >again, running on half-duplex, transfering 100Mb from a client to this >machine (merlin) >on client: >mount -t nfs -o intr,nfsv3,-r=32768,-w=32768 merlin:/freebsd/misc /mnt >dd if=/dev/zero of=/mnt/zero bs=16k count=64x100 >104857600 bytes transferred in 12.765062 secs (8214422 bytes/sec) Decent. > input (fxp0) output > packets errs bytes packets errs bytes colls > 11 0 668 11 0 412 0 > 6 0 1670 5 0 1556 0 > 8 0 180 7 0 0 0 > 11 0 5155696 8 0 62530 0 > 254 0 7015588 23 0 98848 32 > 6115 0 7926312 540 0 118592 1189 > 5304 0 9183810 548 0 136772 1030 > 5768 0 8091074 586 0 120418 1139 > 6527 0 9191418 674 0 138720 1337 > 5915 0 8728739 612 0 129630 1176 > 6492 0 9032044 678 0 133856 1243 > 6195 0 8112222 634 0 122300 1237 > 6509 0 9251329 674 0 137258 1287 > 5886 0 8317303 605 0 125380 1138 > 6490 0 8904250 665 0 132046 1334 > 5978 0 8857169 617 0 139924 1149 > 6444 0 853656 676 0 23624 1259 > 4720 0 313 564 0 0 903 > 1 0 1349 1 0 1390 0 > 2 0 171 0 0 90 0 Well, the volume is on the input side here. The figures say that for any output packet your NIC needs on average about two attempts to get it to the wire. This is almost OK as this is the response channel, and in relation to the overall load of the link (input plus output) the collision rate is not outrageous. Say, some 13%, but for a saturated half-duplex port this is what one would expect. Bear in mind that the numbers you gave us before (top of mail) give a different picture: input and output were not *that* much different, yielding in a much higher overall collision rate. Anyhow. This clearly shows that the slowliness has nothing to do with the network which is just perfect. But you certainly would want to talk to the switch admin to change the port to full-duplex. This is a definitive barrier here and changing that will give you noticeable extra performance. Frankly, forcing a switch that can do full-duplex to half-duplex is plain nonsense as it doesn't really exploit the hardware capabilities. If you've got surplus money, better spend it elsewhere than buying unused capabilities. >Has anybody ever seen something like that ? In networking, you'll see all sorts of strange counters, dubious claims, obscure side-effects, and marvellous breakages. Basically you learn to trust your own eyes and fingers only. :-) Helge To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-stable" in the body of the message
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