Netperf and SMP - Oddness (Part 1 of 2)

Netperf seems to still be a fairly standard network performance tool. I see iperf out there as well, and interestingly enough, it generates very different numbers from netperf.

I've decided to go with netperf for my benchmarking needs, and have started running some simple tests with it to become more familiar with it's operation.

The first oddness I notice is with SMP. I get wildly different results depending on if multiple CPU's are used.

Let's start with what I'm running on: FreeBSD 8.1 AMD64 on a Dell 1850 PowerEdge, with 2 Xeon 5340 CPU. These machines have 2 Intel 1000MT NICs built into the board, which I have given 192.168.88.1 and 192.68.88.2 to. They run the em0 driver.  I've connected them together with a cross-over cable.

FreeBSD is setup as stock, installed from the CD, no changes.

I'm using cpuset to drive the applications to one CPU or the other. Here's what I'm executing;

cpuset -c -l 0 netserver -L 192.168.88.1 -n 2

cpuset -c -l 0 netperf -H 192.168.88.1 -L 192.168.88.2 -t TCP_STREAM -l 300

By specifying the different IP's, I'm forcing the data to move from one NIC to the other. It's running IPv4, not IPv6.

This combination drives both the receive server (netserver) and the test program (netperf) from the same CPU. If I want to make them run on different CPU's I'd change one of the -l 0's to -l 1. If I want to leave it up to the kernel to schedule, I leave out the cpuset command entirely.

All hyperthreading is turned off. These are two standalone CPU's.

Here's what I'm getting, expressed in GigaBytes per Sec

Same CPU:  1.05 GB/sec

Different CPU: 0.47 GB/sec

No Preference: 0.88 GB/sec.

Very interesting..

We're looking at 1/2 speed when we run it on different CPU's. When we don't set a preference for the CPU, it will flip-flop between the two, sometimes both on one, other times separate. The speed for the no preference is almost exactly a split of the single CPU and dual CPU speeds.

I've researched this online, and found a few other people mentioning similar issues, but the threads never come to a conclusion.

There are two reasons I can think of this wide spread between single and dual CPU speeds;

1) Because all the work is happening on one CPU, there is some sort of cache/memory/buffer combining that allows for a faster transfer of data on the PCI bus. Maybe the data isn't transferring - but I do see the little link lights blinking away furiously when I run the tests.

2) There is significant overhead between the processors for SMP.


I do have a second identical PowerEdge 1850 that I plan on bringing into this equation shortly to try and figure out where this is coming from.  By sending to a separate machine, I'm going to eliminate the possibility that the CPU is combining something.

However, if you're looking to make a firewall run quickly, it looks at from this first small test that a single CPU firewall will outperform a dual.  That's an early conclusion, and I'll post more shortly when I know more.

If anyone has more info on this, that would be great.

Continued here..


http://christopher-technicalmusings.blogspot.com/2010/12/netperf-and-smp-oddness-part-1-of-2.html

Switching to OpenBSD from FreeBSD for the new pf syntax

There is a new syntax available for pf in OpenBSD 4.7 and 4.8 that is quite interesting. You can read a bit more about it here;

http://marc.info/?l=openbsd-misc&m=125181847818600

The item that has me the most interested is the new NAT featureset. They've changed it so when you do NAT in the firewall rules, it appears to change the address on the fly to the new IP.

This makes matching rules further down in the ruleset more interesting, and in my mind, clearer, because as you run through the ruleset, you're not going to be concerned with pass rules for both the WAN and LAN addresses - The LAN address will become the WAN address, so there really is just the one rule.


It looks like it will be a while before FreeBSD picks up the new syntax. Currently plans are to update FreeBSD-9.0 to OpenBSD 4.5's version of pf. If you want to play with it, you'll need OpenBSD for now.

Since I'm designing a pretty hefty dual redundant firewall from scratch, complete with ALTQ, pfsync, OpenVPN, load balance, fail over, and some monitoring tools, I'm firing up a OpenBSD 4.8 box now to check it out, and see if it's really as good as it seems.

BTW, here is a link to a conversion script that should help you connvert to the new format:

http://jim-code-rand.blogspot.com/2010/05/openbsd-47-release-pfconf-conversion.html


I'll report back as I make progress. Since I have 2 identical Xeon machines to act as a firewall, I may have a chance to do a small performance test between OpenBSD and FreeBSD. I'm not sure where the advantage will be. I have a lot of faith in FreeBSD, but I also know that ALTQ and pf is a port in FreeBSD, where in OpenBSD they are built in, and have a few more features.


Time will tell.

If anyone else has recently made the switch, I'd love to hear about it..

Porting ICC to FreeBSD

I'm intrigued at the possibility for more speed out of FreeBSD by using Intel's C compiler. It's demonstrated some impressive benchmarks against gcc in the past, and we all know the version of gcc (4.2.1) that is included in FreeBSD 8.x (due to GPL license issues) is quite old, and doesn't properly recognize a Core2 let alone an i7 or Atom processor.

Here's my posting to the freesbsd-ports mailing list;

--

My first stage on this will be feasibility. I'm a pretty busy guy, so I don't want to waste time on a task that I won't complete. I'll either do it all, or I won't bother. It should take me a few weeks to get enough of a feel for things to make that call.

Fist stage is working with ICC on Linux to make sure I understand how it behaves. I don't think it will matter which distro too much, but if anyone has a suggestion, I'm open to it. I'll be able to do some basic comparisons with a newer GCC at the same time... or perhaps I'll go back in time to an older distro that has GCC 4.2.1 for a closer comparison to what FreeBSD has.

I'll be focusing on 64 bit FreeBSD only, and I'll work it from the 8.1 base. 9 is too much of a moving target.

At this stage, I'm not sure if I should bother with kernel or not. Unfortunately, unless someone has benchmarks showing the difference a FreeBSD kernel/world compiled with ICC is on a modern Intel Xeon or i7, I really don't know if it's worth it or not. I'll probably have to do it to see if it's worth it.

Personally, I'm interested in anything that can help make my ZFS installations move faster. I'm building them with 96+ gigs of RAM for L2ARC, so memory alloc, etc are important, along with checksum and compression calculations - Items that I know are improved in newer Intel chips. Is GCC/LLVM able to access them as well as ICC? Does it matter to real world speed if I can get 20% more out of them? We'll see.

My processor will probably be an i7, ultimately I can probably pull a spare production X5660 for a few days worth of testing later on.

I feel a modern processor is necessary so it's new features can be properly exploited. I expect that there should be less of a difference between ICC and GCC on older base P4 type architecture, but once again, that's something that I can test and report on.

Any comments or suggestions are welcome.

ESXi 4.0.0 vs 4.1 Speed - 4.1 Not as fast

I've just upgraded my 4.0.0 ESXi box to 4.1.

...Well, lets not call it upgrading, the process I used was to pull my existing boot drive, install a new 8 gig  USB stick inside my Dell T710, and install a fresh copy of the Dell Installable 4.1 ESXi. This results in a fresh copy, and all I have to do is reattach my storage, import my .VMX files, and I'm back in business.

I once had a bit of a mess with the upgrade process from 3.0 to 3.5, so I settled on this method as being he safest. I even pull my drives when I do the upgrade, so there is no chance the installer will become confused and format my main datastore. Am I paranoid? It's happened before, and you only have to burn me once..

The process isn't that much more time consuming than an in-place upgrade. When your ESXi files are all on one drive/flash stick, and your datastores are all on another, you've got plenty of flexibility. I was able to do it within 30 minutes, because I really don't edit my ESXi configuration that much from default.

 I'm very interested in 4.1 because it has some neat power management interfaces. Look here, I can now track my wattage being burned on this server:

This is for a Dell T710 with 24 gig DDR3 memory, 2 Xeon 5660's,  4 600Gig SAS drives, and 4 1TB nSAS drives. I've yet to check how accurate this is with a KilloWatt or similar meter, but this sounds about right.


I'm also interested in memory compression - When you building redundancy by having two ESX servers, you need to have very similar configurations for processor / memory on your backup server, or you take a large performance hit. That's not always easy to budget for. If I can get away with my Exchange servers still running for a couple of hours on a server that is only 1/2 or 1/4 the memory of my main ESX, then I'll be happy. It's got to be quicker to compress memory than to swap it to disk - We'll see. I'll be testing that later on.

Service Console is now no longer an unsupported hack.

But really, the bit that gets me very interested the most is that vmware is now putting it's full weight behind ESXi - There won't be any more ESX! And to make this transition easier, you can now access vMotion from an ESXi 4.1 server. You still need licenses, but now it's nearly $10k cheaper to access this technology.

With my Ghetto-SAN comming online any week now, I'm very excited about this development.

BUT - There seems to be a but of a trade-off for the new things that 4.1 brings - It's just a tad slower than 4.0.0.

Once again, I do quick and dirty benchmarks to get a feel for things - Performance Test 6.1 isn't the best tool, but it's quick and makes for nice easy graphs to compare. After pouring through reams of iozone stats in Excel, I sometimes like quick, easy, and pretty.

My process was simple: Take a Performance Meter tests from a running 2008 R2 server before the upgrade to 4.1, and one after (with the new vmware tools loaded).

While 4.1 had better graphic performance (who cares!), it was around 2% slower for memory and CPU performance.

That's a small price to pay for new features, and I'm hoping it's just a result of new technology being focused on stability first, performance second.

Anyone else run benchmarks that can confirm or deny this?

ZFS and NFS performance, with ZIL disable and/or flushcache

I'm building my new FreeBSD 8.1 SAN, and one of the first tasks is trying to pull decent NFS performance from the box.

As you may be aware, NFS and ZFS don't mix well. It's because NFS is asking for a flush of the ZFS ZIL after each write, which is incredibly slow. It destroys all caching or other speed enhancements that ZFS can bring to the table.

The quick and dirty response is to disable the ZIL. While this won't lead to corruption, it's removing one of ZFS's protection mechanisms, and as I'm building a very large SAN, I really don't want to hamper ZFS's ability to save my ass on data corruption issues.

This is basically opening NFS in async mode, which is what iSCSI does. I want iSCSI performance with the stability of NFS sync.

I thought I'd play around with disabling the ZIL (makes me nervous), using  loander.conf commands, and adding a SSD as the ZIL.

NFS Tests on a ZFS RAID10

Notes:
All numbers are MB/sec, tests run twice (thus 2 numbers) then rebooted.
Tests are from PerformanceTest 6.1, which is easy for quick-n-dirty testing.
Tests are on a Windows Server 2003 32 Bit, going to FreeBSD 8.1, but who cares? They are only valid as a comparison on my own machine.  

Without ZIL
Fileserver: 64.25, 65.97 MB/sec
Workstation:  9.52, 12.99
Database: 56.31, 56.98



Decent speed for a RAID-10 ZFS on SATA drives without any tweaking. Beats my C: drive which is a SAS RAID-10 under ESXi, and is around the same speed as I was getting from iSCSI

With ZIL
Fileserver:  8.37, 6.53  
Workstation: 2.51
Database:

Basically: Much, Much slower.  I gave up after a few tests, as it was so tedious I didn’t want to continue. I did these tests before, so I know it’s slower across the board. At this speed iSCSI kicks NFS's ass. 

NOTE: I did try with ZIL and vfs.zfs.cache_flush_disable=1 , but the speed is basically just as bad. Besides, why wouln't you want your ZIL on a SSD?


With ZIL on Intel X25-M SSD (32 Gig)
Fileserver: 61.38, 62.08
Workstation: 8.05, 7.66
Database:  23.07, 23.05

Hmm,this is faster. I wouldn't be too unhappy with this type of performance. Database still suffers though.
 

With ZIL on Intel X25-M SSD (32 Gig), vfs.zfs.cache_flush_disable=1
Fileserver 54.69, 62.57
Workstation 12.43, 9.54
Database  54.2, 54.69

Hey - That's pretty good. Just a tiny tad under ZIL-less operation. 

Notes for SSD tests: The SSD as ZIL stayed around 50% busy. The ZIL does work.

So all we have to do is make ZFS lie and say it flushes the cache when it doesn't. Editer your /boot/loder.conf to include the vfs.zfs.cache_flush_disable=1 command, and you're off and running.

I believe this is an enhancement in newer ZFS pools anyway, so I'm really not too worried about it. If it's on the ZIL, why do we need to flush it to the drive? A crash at this point will still have the transactions recorded on the ZIL, so we're not losing anything.

BTW - It looks like ZFS v23 is comming to FreeBSD sooner than we expected - So this may all be moot, as it's included around v18 I seem to recall. 

Final thoughts: Never, never run a ZIL that isn't mirrored. It dies, lots of bad things happen... although I was able to shut down the system, turn off my ZIL in loader.conf, and boot without the SSD, so I think you could recover.. I'll be testing how nasty things are with a destroyed ZIL during transactions tomorrow.

FreeBSD, pf, and fwanalog

I think I've fixed this - if anyone was trying to run it and getting nonsense. There were some issues with the tcpdump date format, a couple small bugs, etc.

I'll eventually post a patch, but for now just ask if you're having the same problems, I'll send you the updated fwanalog script.

OpenSolaris: So close...

I posted earlier of my love for ZFS Dedup, and how I was experimenting with OpenSolaris as a new base-unix instead of FreeBSD, because FreeBSD is so far behind in the ZFS ports.

Well, I'm switching back. It's been a few months, and we still don't see any new OpenSolaris code. Will Oracle release a new OpenSolaris? There's talk about it being dumped. There's too many questions, so I have decided to side-line and wait - so I'm back to FreeBSD until I see an OpenSolaris 2010 - But it's quite possible we'll have FreeBSD Dedup before we have another solid OpenSolaris release.

Quick and Dirty: FreeBSD 8.1 AHCI vs ATA (CAM)

While building and testing what will be a 24 drive SAN running FreeBSD 8.1, ZFS, and NFS/iSCSI I discovered a problem with hot-swapping the SATA drives.

It seems FreeBSD 8.1 AMD64 was running the SATA drives in ATA mode, so they really didn't hot-swap. If I pulled a drive and reinserted, I couldn't make it understand that the drive was back, even if I fooled with atacontrol's attach and detach. I had to reboot, which is no way to run a SAN, no mater how ghetto it may be.

A bit of poking showed that while my BIOS was set to AHCI (Intel ICH7R chipset), FreeBSD was still running in ATA mode. (type 'atacontrol list' and if you see drives, you are too). camcontrol is the program you use once in CAM mode.

The answer was to put ahci_enable="YES" in /boot/loader.conf.

This changes your drives to ada's from ad's which causes a boot problem, but that's easily fixed.

I did a quick a dirty test with 'raidtest' to show the speed difference. Here's my raidtest creation command:

raidtest genfile -s 128 -S 512 -n 50000

Here's the results:

With CAM: (ahci_enable="YES" in /boot/loader.conf)

iscsi# raidtest test -d /dev/zvol/tank/vol
Read 50000 requests from raidtest.data.
Number of READ requests: 24831.
Number of WRITE requests: 25169.
Number of bytes to transmit: 3286713344.
Number of processes: 1.
Bytes per second: 37162958
Requests per second: 565


Without CAM

iscsi# raidtest test -d /dev/zvol/tank/vol
Read 50000 requests from raidtest.data.
Number of READ requests: 24831.
Number of WRITE requests: 25169.
Number of bytes to transmit: 3286713344.
Number of processes: 1.
Bytes per second: 6069384
Requests per second: 92


Big difference eh? It's night and day. It then lead to some ZFS issues when I turned CAM on, because ZFS likes to hit write/read stalls when you move a lot of data, but I cleared that up with some further ZFS tweaks that I will detail another day.

If you're not running with ahci_enable="yes" in your loader.conf, you may want to look at enabling it.

I"ll be doing more tests over the new few days on a few different FreeBSD machines, and we'll see what the general results are.

ZFS on FreeBSD 8.1

I've been using ZFS on my FreeBSD box for some time now, and it's been serving out gigs and gigs of data faithfully for some time.

I am looking into OpenSolaris, but with the slow (or never) release of 2010.x I'm still fully a FreeBSD shop at this stage for Unix.

I've just upgraded to 8.1 Release a few days ago, and I'm liking the new release - I took the opportunity to also upgrade my Samba to 3.4.8 at the same time, so the system seems perkier. I didn't have the time to do any real speed tests, so take that for what it's worth.

BUT - I've been getting some "kmem_map to small" panics when I tried to copy down a 160 gig file. I can't recall if I've ever moved such a large file before, so I don't think this is an 8.1 issue.

Some digging around and I found this information on the FreeBSD mailing list that I wanted to pass along.


From: Steve Polyack
Subject: Re: Freebsd 8.0 kmem map too small
Date: Wednesday, May 5, 2010 - 7:46 am


On a system here with 8GB of RAM and a very large zpool consisting of
multiple zdevs, little tuning was needed. The system is running
8-STABLE(amd64) as of a month or two ago. The only things I have set in
/boot/loader.conf are:
vm.kmem_size="12G"
vfs.zfs.arc_max="4G"

Setting kmem_size to 12G came from a combination of recommendations I
saw in various mailing list posts (you can probably dig them up).
Setting it to the physical memory size was the initial recommendation,
while others recommended 1.5x physical memory size to help prevent
fragmentation/wasted space in kmem.

Regardless, this has served us quite well for the ~6 months the system
has been in use. It has never crashed, even under intensive
multi-threaded benchmarking.

Other people recommend vm.kmem_size to be 1/2 of available RAM, and then vsf.zfs.arc_max to be 512M less than that, but that doesn't make sense to me - What's the point of RAM if you can't use it? This box only runs ZFS and Samba, let these things have some memory.

I've now set those same values as Steve on my FreeBSD system in question is running 8 gigs as well. I'm going to start my 160 gig copy again (which BTW, I get ~34 Meg/Sec according to Windows 7)

If you don't hear back from me, it's working well for me. :-)

ZFS Dedeuplication

Oh my god - Is anyone else as excited about this as I am?

Are you thinking of a SAN running a massive ZFS raidz2 in deduplication mode?

I've already built a 6tb raidz2 array last year, and I'm finding I need more space - next shot will be for 12 or 16 tb, and I'd love to use dedup to help me out.

I'm so curious about it, I'm considering switching to Solaris as my disk host. Normally I'd use FreeBSD, but their ZFS is too far behind (version 13, Sun's got Version 22) to support dedup in the next 2 years.

I'll be posting some test results soon.. just experimenting with some 4 gig .OST files under a ZFS dedup scenario to get a feel for compression.

Early tests with straight MP3's showed 23% compression. These are very, very promising times.

Here's a few links you can drool over until you get the time to do something, or I post my results:

http://blogs.sun.com/jsavit/entry/deduplication_now_in_zfs

http://blogs.sun.com/bonwick/entry/zfs_dedup

http://en.wikipedia.org/wiki/Data_deduplication