Great Thread on Network Performance Troubleshooting

Now that FreeBSD 5.3 has arrived, users are trying to determine if any performance issues are caused by their hardware, OS, or applications. There's a great freebsd-stable thread discussing a user's attempt to improve NFS performance. One of Robert Watson's comments is especially useful, since he spells out five steps to troubleshoot network performance:

"I think the first thing you want to do is to try and determine whether the problem is a link layer problem, network layer problem, or application (file sharing) layer problem. Here's where I'd start looking:

(1) I'd first off check that there wasn't a serious interrupt problem on the box, which is often triggered by ACPI problems. Get the box to be as idle as possible, and then use vmstat -i or stat -vmstat to see if anything is spewing interrupts.

(2) Confirm that your hardware is capable of the desired rates: typically this involves looking at whether you have a decent card (most if_em cards are decent), whether it's 32-bit or 64-bit PCI, and so on. For unidirectional send on 32-bit PCI, be aware that it is not possible to achieve gigabit performance because the PCI bus isn't fast enough, for example.

(3) Next, I'd use a tool like netperf (see ports collection) to establish three characteristics: round trip latency from user space to user space (UDP_RR), TCP throughput (TCP_STREAM), and large packet throughput (UDP_STREAM). With decent boxes on 5.3, you should have no trouble at all maxing out a single gig-e with if_em, assuming all is working well hardware wise and there's no software problem specific to your configuration.

(4) Note that router latency (and even switch latency) can have a substantial impact on gigabit performance, even with no packet loss, in part due to stuff like ethernet flow control. You may want to put the two boxes back-to-back for testing purposes.

(5) Next, I'd measure CPU consumption on the end box -- in particular, use top -S and systat -vmstat 1 to compare the idle condition of the system and the system under load.

If you determine there is a link layer or IP layer problem, we can start digging into things like the error statistics in the card, negotiation issues, etc. If not, you want to move up the stack to try and characterize where it is you're hitting the performance issue."

Richard Blum's book Network Performance Open Source Toolkit, which I read and reviewed last year, also gives good tips.

Comments

Post a Comment

Popular posts from this blog

Zeek in Action Videos

Image
This is a quick note to point blog readers to my Zeek in Action YouTube video series for the Zeek network security monitoring project .  Each video addresses a topic that I think might be of interest to people trying to understand their network using Zeek and adjacent tools and approaches, like Suricata, Wireshark, and so on.  I am especially pleased with Video 6 on monitoring wireless networks . It took me several weeks to research material for this video. I had to buy new hardware and experiment with a Linux distro that I had not used before -- Parrot .  Please like and subscribe, and let me know if there is a topic you think might make a good video.
Read more

MITRE ATT&CK Tactics Are Not Tactics

Image
Just what are "tactics"? Introduction MITRE ATT&CK  is a great resource, but something about it has bothered me since I first heard about it several years ago. It's a minor point, but I wanted to document it in case it confuses anyone else. The MITRE ATT&CK Design and Philosophy document from March 2020 says the following: At a high-level, ATT&CK is a behavioral model that consists of the following core components: • Tactics, denoting short-term, tactical adversary goals during an attack; • Techniques, describing the means by which adversaries achieve tactical goals; • Sub-techniques, describing more specific means by which adversaries achieve tactical goals at a lower level than techniques; and • Documented adversary usage of techniques, their procedures, and other metadata. My concern is with MITRE's definition of "tactics" as "short-term, tactical adversary goals during an attack," which is oddly recursive. The key word in the tacti
Read more

New Book! The Best of TaoSecurity Blog, Volume 4

Image
  I've completed the TaoSecurity Blog book series . The new book is  The Best of TaoSecurity Blog, Volume 4: Beyond the Blog with Articles, Testimony, and Scholarship .  It's available now for Kindle , and I'm working on the print edition.  I'm running a 50% off promo on Volumes 1-3 on Kindle through midnight 20 April. Take advantage before the prices go back up. I described the new title thus: Go beyond TaoSecurity Blog with this new volume from author Richard Bejtlich. In the first three volumes of the series, Mr. Bejtlich selected and republished the very best entries from 18 years of writing and over 18 million blog views, along with commentaries and additional material.  In this title, Mr. Bejtlich collects material that has not been published elsewhere, including articles that are no longer available or are stored in assorted digital or physical archives. Volume 4 offers early white papers that Mr. Bejtlich wrote as a network defender, either for technical or pol
Read more