IBM REDP-4285-00 4.7.2 Speed and duplexing

4285ch04.fm Draft Document for Review May 4, 2007 11:35 am

126 Linux Performance and Tuning Guidelines

netstat, tcpdump and ethereal are useful tools to get more accurate characteristics (Refer to

2.3.11, “netstat” on page53 and 2.3.13, “tcpdump / ethereal” on page 55).

4.7.2 Speed and duplexing

It may sound trivial but one of the easiest ways to improve network performance is by

checking the actual speed of the network interface because there can be issues between

network components (such as switches or hubs) and the network interface cards. The

mismatch can have a large performance impact as shown in Example 4-17.

Example 4-17 Using ethtool to check the actual speed an duplex settings

[root@linux ~]# ethtool eth0

Settings for eth0:

Supported ports: [ MII ]

Supported link modes: 10baseT/Half 10baseT/Full

100baseT/Half 100baseT/Full

1000baseT/Half 1000baseT/Full

Supports auto-negotiation: Yes

Advertised link modes: 10baseT/Half 10baseT/Full

100baseT/Half 100baseT/Full

1000baseT/Half 1000baseT/Full

Advertised auto-negotiation: Yes

Speed: 100Mb/s

Duplex: Full

From the benchmark results shown in Figure4-15, note that a small data transfer is less

impacted than a larger data transfer when network speeds are incorrectly negotiated.

Especially data transfers larger than 1KB shows the drastic performance impact (throughput

declines 50-90%). Make sure that the speed and duplex are correctly set.

Figure 4-15 Performance degradation caused by auto negotiation failure

Numerous network devices default to 100 Mb half-duplex in case of a minor mismatch during

the auto negotiation process. To check for the actual line speed and duplex setting of a

network connection, use the ethtool command.

Note that most network administrators believe that the best way to attach a network interface

to the network is by specifying static speeds at both the NIC and the switch or hub port. To

100Mbsp half duplex

0.01

0.10

1.00

10.00

100.00

1,000.00

1024 2048 4096 8192 16384 32768 65536 131070 262144

socket sizes

Mbytes/sec

1

16

128

1K

4K

16K

32K

64K

128K

Response

data size

1Gbps full duplex

0.01

0.10

1.00

10.00

100.00

1,000.00

1024 2048 4096 8192 16384 32768 65536 131070 262144

socket size

Mbytes/sec

1

16

128

1K

4K

16K

32K

64K

128K

Response

data size

Contents

Main Page Page Page Contents Page Page Page Notices Trademarks Preface How this Redpaper is structured The team that wrote this Redpaper Become a published author Comments welcome Page operating system Page 1.1 Linux process management 1.1.1 What is a process? 1.1.2 Lifecycle of a process 1.1.3 Thread 1.1.4 Process priority and nice level Process priority 1.1.5 Context switching CPU 1.1.6 Interrupt handling Suspend Resume 1.1.7 Process state Processor Zombie processes 1.1.8 Process memory segments Text Data Stack Process address space 1.1.9 Linux CPU scheduler 4285ch01.fm 10 Figure 1-8 Linux kernel 2.6 O(1) scheduler via scheduler_tick() P active expired array[0] array[1] PP P active expired array[0] array[1] PP Parent Child 1.2 Linux memory architecture 1.2.1 Physical and virtual memory Virtual memory addressing layout 32-bit Architecture 64-bit Architecture User space Kernel space 32-bit Architecture 64-bit Architecture User space Kernel space 1.2.2 Virtual memory manager Page frame allocation Buddy system Page frame reclaiming cache and process address space. The page cache is pages mapped to a file on disk. The swap 1.3 Linux file systems 1.3.1 Virtual file system 1.3.2 Journaling 1. write journal logs write File system Journal area 1.3.3 Ext2 Ext2 1.3.4 Ext3 Mode of journaling 1.3.5 ReiserFS 1.3.6 Journal File System 1.3.7 XFS 1.4 Disk I/O subsystem 1.4.1 I/O subsystem architecture 1.4.2 Cache Memory hierarchy Locality of reference Flushing dirty buffer 1.4.3 Block layer Disk Cache Disk Cache Block sizes 1.4.4 I/O device driver SCSI ips qla2300mptscsih 1.4.5 RAID and Storage system st sr_modsd_modsg scsi_mod Upper level driver Mid level driver Device Process Low level driver 1.5 Network subsystem 1.5.1 Networking implementation Socket buffer TCP/IP IPX Appletalk DEVICE NAPI way NAPI way DEVICE Netfilter Netfilter Connection tracking 1.5.2 TCP/IP Connection establishment Chapter 1. Understanding the Linux operating system 31 Draft Document for Review May 4, 2007 11:35 am 4285ch01.fm Figure 1-27 TCP 3-way handshake Client Server 4285ch01.fm 32 Traffic control TCP/IP transfer window CLOSED LISTEN SYN SENT LAST-ACK ESTAB SYN RCVD 1.5.3 Offload 1.5.4 Bonding module 1.6 Understanding Linux performance metrics 1.6.1 Processor metrics 1.6.2 Memory metrics 1.6.3 Network interface metrics 1.6.4 Block device metrics transfers per second metric in conjunction with the kBytes per second value helps you to Page Page Page 2.1 Introduction 2.2 Overview of tool function 2.3 Monitoring tools 2.3.1 top 2.3.2 vmstat 2.3.3 uptime 2.3.4 ps and pstree Page Thread information 2.3.5 free Memory used in a zone 2.3.6 iostat Page 2.3.7 sar 2.3.8 mpstat 2.3.9 numastat 2.3.10 pmap 2.3.11 netstat 2.3.12 iptraf 2.3.13 tcpdump / ethereal tcpdump ethereal 2.3.14 nmon 2.3.15 strace 2.3.16 Proc file system Page 2.3.17 KDE System Guard Work space System Load Process Table Configuring a work sheet Page 2.3.18 Gnome System Monitor 2.3.19 Capacity Manager Page Page 2.4 Benchmark tools 2.4.1 LMbench 2.4.2 IOzone 2.4.3 netperf Page Page 2.4.4 Other useful tools bottlenecks 3.1 Identifying bottlenecks 3.1.1 Gathering information Page 3.1.2 Analyzing the servers performance 3.2 CPU bottlenecks 3.2.1 Finding CPU bottlenecks 3.2.2 SMP 3.2.3 Performance tuning options 3.3 Memory bottlenecks 3.3.1 Finding memory bottlenecks Paging and swapping indicators 3.3.2 Performance tuning options 3.4 Disk bottlenecks 3.4.1 Finding disk bottlenecks vmstat command iostat command 3.4.2 Performance tuning options 3.5 Network bottlenecks 3.5.1 Finding network bottlenecks Page 3.5.2 Performance tuning options Page Page 4.1 Tuning principals 4.1.1 Change management 4.2 Installation considerations 4.2.1 Installation Page 4.2.2 Check the current configuration dmesg Page ulimit 4.2.3 Minimize resource use Daemons Page Page Page Changing runlevels Limiting local terminals 4.2.4 SELinux SELinux Kernel Process User Request Access Grant Access Grant/Deny Access Based on Policy 4.3 Changing kernel parameters Page Page 4.3.1 Where the parameters are stored 4.3.2 Using the sysctl command 4.4 Tuning the processor subsystem 4.4.1 Tuning process priority 4.4.2 CPU affinity for interrupt handling 4.4.3 Considerations for NUMA systems numactl 4.5 Tuning the vm subsystem 4.5.1 Setting kernel swap and pdflush behavior 4.5.2 Swap partition 4.5.3 HugeTLBfs 4.6 Tuning the disk subsystem 4.6.1 Hardware considerations before installing Linux Number of drives Guidelines for setting up partitions 4.6.2 I/O elevator tuning and selection Selecting the right I/O elevator in kernel 2.6 Page Impact of nr_requests Page Impact of read_ahead_kb 4.6.3 File system selection and tuning Using ionice to assign I/O priority Access time updates Select the journaling mode of the file system Block sizes stripe size of the array (or segment in the case of Fibre Channel). The stripe-unit size is the 4.7 Tuning the network subsystem 4.7.1 Considerations of traffic characteristics 4.7.2 Speed and duplexing 4.7.3 MTU size 4.7.4 Increasing network buffers Tuning window sizes Page Impact of socket buffer size 4.7.5 Additional TCP/IP tuning Tuning IP and ICMP behavior Page Tuning TCP behavior Tuning TCP options Chapter 4. Tuning the operating system 133 Draft Document for Review May 4, 2007 11:35 am 4285ch04.fm Figure 4-19 Netfilter rules applied 4.7.6 Performance impact of Netfilter Figure 4-18 No Netfilter rule applied TCP_CRR benchmark TCP_CRR benckmark TCP_CRR benchmark 4.7.7 Offload configuration Impact of offloading Chapter 4. Tuning the operating system 135 Draft Document for Review May 4, 2007 11:35 am 4285ch04.fm Figure 4-21 Throughput degradation by offloading Figure 4-20 CPU usage improvement by offloading cpu usage improvement - default vs offload off 4.7.8 Increasing the packet queues 4.7.9 Increasing the transmit queue length 4.7.10 Decreasing interrupts Page Page Page 4285ax01.fm 140 Hardware and software configurations Linux installed on guest IBM z/VM systems Linux installed on IBM System x servers Three IBM System x x236 servers were configured as shown in TableA-2. Page Page Abbreviations and acronyms 4285abrv.fm 144 Related publications IBM Redbooks Other publications Online resources Page How to get IBM Redbooks Help from IBM Page Index Symbols Numerics A B E F G H I N O P 4285IX.fm 152 Q R S T U V W X Z Page Page Redpaper Back cover INTERNATIONAL TECHNICAL SUPPORT ORGANIZATION Linux Performance and Tuning Guidelines