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1
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2answers
29 views

Is cmp faster than diff -q?

In a recent AU question on checking whether some files have differing content, I saw a comment stating that if the differing sections didn't matter, cmp would be faster than diff. This SO answer ...
1
vote
1answer
24 views

blktrace - differentiating between sequential to random io

I'm looking for a way to determine whether an app is doing sequential or random I/O. Is it possible to look at a blktrace capture and say if I/O is sequential or random? If yes, any examples of what ...
2
votes
0answers
44 views

Why iperf still reports 1Gbps performance when using bonding over two 1Gbps adapters?

As I understand it, bonding brings among other benefits the ability to increase the network speed between two machines in a LAN. Bonding [...] means combining several network interfaces (NICs) to ...
2
votes
1answer
31 views

How to test Disk IO on VMs with iozone?

I want to test the disk IO performance like read, write, random read, random write and so on both in physical machine and VMs (with aufs file system). Also I want to test the throughput performance in ...
0
votes
0answers
13 views

Why would attempts to bind affinities for rcu kthreads fail?

I am trying to get full tickless mode working on my box on Ubuntu kernel 3.10.39. I am running the following command: for i in `pgrep rcu` ; do taskset -pc 0 $i ; done It seems to work on some of ...
1
vote
1answer
21 views

why doesn't iozone generate output file?

I'm using iozone3 for tesing, on Xamin (an Debian-based OS). When I enter iozone command, for example iozone -Rab output.xls, the test runs successfully. But after running the test (after displaying ...
0
votes
3answers
39 views

dd write vs read performance

I have recently done some performance tests on a new server (using dd) and wonder why read performance is so much worse than write performance? Shouldn't it be another way around? file size was in ...
4
votes
6answers
152 views

grep with a lot of files which contains a lot of lines?

Imagine we have a lot of huge(30000 line)files: a.2014-05-06, a.2014-05-07, a.2014-05-08 and so on. I know that we can grep a line with word using this command: grep "word" a.* First I guess this ...
2
votes
1answer
119 views

How much speed difference for a tweaked bios versus uefi boot? [closed]

EFI can be faster, but that's not certain. The biggest speed difference is in hardware initialization early in the process. On my systems, this is a fraction of the total boot time, so a ...
0
votes
2answers
74 views

Authentication very slow (both with ssh and su)

I'm having a problem on one of our production servers where the login attempts become progressively slower as time passes. After roughly 5 days it becomes so slow that some critical processes/cron ...
0
votes
0answers
32 views

Ubuntu 13.10 x64 - slow and acting strangely gvfs+NTFS

I have updated Ubuntu 13.10 x64 to latest stable releases of all packages. I'm running GNOME and using SSD disks on USB 3.0 ports in lenovo Y500 notebook. I'm using Midnight Commander (as root) in ...
0
votes
1answer
67 views

Lower cpu performance in Linux [closed]

I have a problem with my CPU performance in Linux. I have a laptop, Toshiba Satellite C660-101. Despite the fact that the CPU works perfectly fine in Windows 7, Linux has some serious issues. ...
0
votes
1answer
38 views

RAID Level 5 versus Level 1

Is it slower to write one block in RAID Level 5 with 5 disks than RAID 1 with two disks (mirroring only)? I think No since with Level 5 you are writing the data and the parity (two writes). With Level ...
2
votes
2answers
65 views

Will grep go faster with line breaks?

I have some big files that I have changed into "standardized form", removing line breaks. I want to speed up greps on those files. I know that you can optimize grep by doing grep 'partofpattern' | ...
15
votes
2answers
391 views

Is dash or some other shell “faster” than bash?

I always thought that the only benefit of using dash instead of bash was that dash was smaller, and therefore many instances of dash would start faster at boot time. But I have done some research, ...
7
votes
2answers
454 views

Why is `tac file | grep foo' (piping) faster than `grep foo < <(tac file)' (process substitution)?

This question was motivated by "Reverse grepping", about grepping a huge file from bottom up. @chaos said: tac file | grep whatever Or a bit more effective: grep whatever < <(tac file) ...
0
votes
0answers
21 views

Can ramdisk improve performance when stats show low wait and system cpu use?

I have jobs that do I/O of rates peaking around 200mb/s. On high load (over twice cpu cores) I tried to copy large file and got only few mb/s. Gathered dstat show single digits in wai and sys category ...
3
votes
1answer
61 views

Artificially prime buffer cache?

Is it beneficial to artificially prime the buffer cache when dealing with larger files? Here's a scenario: A large file needs to be processed, line by line. Conceptually, it is easy to parallelize ...
6
votes
2answers
127 views

Reduce bad block retry / wait times in Ubuntu

How can I reduce the IO wait time and retry times so that the OS doesn't continually try to write to a failing drive? I have an system that I use to make copies of demo content that gets loaned out ...
1
vote
0answers
10 views

Ubuntu with LAMP+Mediawiki suffering spikes

I'm sorry if this question is off topic, but I'll give it a shot: I have a VPS running Ubuntu 12.04, a LAMP stack, and Mediawiki. After installing Mediawiki I noticed that my wiki site was spiking, ...
1
vote
1answer
53 views

Slow Linux machine [closed]

Every time I login (via ssh) in my Linux/debian computer it takes too long for the password prompt to appear. Also, every time I try to run a python script or a tcpdump it takes too long until it ...
9
votes
1answer
62 views

Limit on the number of btrfs snapshots?

I am considering using btrfs on my data drive so that I can use snapper, or something like snapper, to take time based snapshots. I believe this will let me browse old versions of my data. This would ...
2
votes
0answers
39 views

Cgroups - memory subsystem

I want to set the memory.limit_in_bytes parameter for a control group and disable OOM, so processes freeze when the limit is reached. But i want to change that limit dynamically, if there is more ...
3
votes
2answers
68 views

Testing the Success of a Congestion Algorithm

How do you test whether a particular congestion algorithm is working for you? I ask because it's not as if I can easily re-create a representative workload for most algorithms. I'm current looking at ...
1
vote
0answers
31 views

apache mod_security and performance

I have a list of bots to block, so I was thinking that fail2ban could be a solution until I realized that mod_security would be more efficient in this kind of tasks. The number of bots is huge, so ...
0
votes
0answers
41 views

OTG musb and full speed bulk endpoint throughput

We are developing an application on an OMAP3 device (DM3730 ti). An acquisition board gets samples and sends them to the OMAP board via USB. This acquisition board does a 16KHz sampling which ...
3
votes
3answers
77 views

Advantages to uploading files to /tmp before moving off to permanent storage?

It seems the common trend in programming when building functionality for handling file uploads is to have the file first uploaded to a temporary directory/folder (e.g. /tmp on Linux). Once the file ...
2
votes
0answers
62 views

Does ionice work with the deadline scheduler?

My Debian Wheezy systems use the deadline scheduler. I'm accustomed to using ionice to reschedule the I/O priority of disk-intensive jobs at busy times, and anecdotally this seems to help (but I ...
1
vote
0answers
44 views

Do kernel threads seem to interfere with full tickless mode?

I'm trying to disable local timer interrupts for low latency. I have full tickless mode enabled in the kernel config and I have the boot parameter nohz_full set for the cores in question. However ...
2
votes
1answer
263 views

Very high CPU load, but nothing significant in top

I'm running Ubuntu Linux 12.04.1, with VirtualMin 4.08.gpl GPL and 2 CPU cores. Pretty much all the time for the last few weeks, it's been running at well above load average of 5, usually up closer ...
0
votes
1answer
110 views

How do I create a RAM disk on Linux Mint?

I am running a package that adds data to the end of 140–300 files each time through the process. I'm thinking of moving the process to a RAM disk, and using rsync to copy it back when done. My goal ...
7
votes
3answers
851 views

What are the exact differences between awk and cut with grep? [closed]

We know that we can get the second column of the line we want from a file using these two techniques: awk '/WORD/ { print $2 }' filename or grep WORD filename| cut -f 2 -d ' ' My questions are: ...
1
vote
2answers
186 views

Very poor read performance compared to write performance on md(raid1) / crypt(luks) / lvm

I'm experiencing very poor read performance over raid1/crypt/lvm. In the same time, write speeds are about 2x+ faster on the same setup. On another raid1 setup on the same machine I get normal read ...
0
votes
0answers
30 views

If a buggy application underperforms, it it possible server tuning could have no affect?

To set the stage, imagine if you will: A read-heavy Tomcat Application with MySQL on Red Hat Enterprise Linux with some problematic Java Class files which resulted in the application performing a ...
1
vote
0answers
68 views

Monitoring Disk Latency

We have quite a few physical machines in our environment, yet we have no trending data over a period of time for disk latency statistics. We can easily run the standard iostat commands to see what the ...
3
votes
2answers
260 views

What is the expected performance of obnam? Or: why is it so slow?

I've been playing around with obnam these last few days, and although it looks very promising and seems to offer basically everything I ever wanted in a backup tool, I am pretty disappointed in its ...
1
vote
1answer
128 views

CPU Placement in KVM

I have a configuration of KVM guests where the cpu placement is configured as follows: <vcpu placement='static'>1</vcpu> Now since I don't have a cpuset specified I was reading libvirt ...
0
votes
1answer
102 views

Is it useful to setup RAID0 on laptop? [closed]

I have a Dell laptop, which I am going to replace the CD-ROM hub with a HDD. I am thinking if I setup a RAID0 on my original HDD and the new HDD, would I have some I/O performance improvement? ...
1
vote
1answer
47 views

How does downloading speed vary between download managers? [closed]

I used several download managers on Ubuntu and found variation in downloading speed. uGet (recommended) Flareget xdm (Xtreme Download Manager) Steadyflow I find variation in downloading speed. My ...
3
votes
1answer
99 views

Performance differences between pipelines and process substitution

I tend to use pipelines in my bash scripts over process substitution in most situations, especially in cases of using multiple sets of commands as it seems more readable to do ... | ... | ... over ... ...
2
votes
1answer
110 views

speed up linux server [closed]

On my VPS, I have centOS 6.5 installed with 2 virtual cpu 2048 MB memory, 60 GB disk and 300 GB monthly data. Doing a speed test today resulted in 168.62 Mbit/s dload and 37.39 Mbit/s upload. Then my ...
3
votes
2answers
307 views

Large ext4 partition ridiculously slow when writing

We have four identical Linux servers with a large (5T) hard disk partition. We have Scientific Linux with this kernel: Linux s3.law.di.unimi.it 2.6.32-358.18.1.el6.x86_64 #1 SMP Tue Aug 27 14:23:09 ...
1
vote
0answers
42 views

is star faster than GNU and BSD tar? [closed]

I made serveral runs (create a tarball) on OS X Mavericks with BSD tar, GNU tar and star. star is always the winner. System is iMac (Mid 2010) only running Terminal. root@time var> du -sh log/ ...
3
votes
2answers
178 views

How to record the actual running time of a program with other programs running? [duplicate]

When timing the wall time performance of an OpenMP program on Linux while other programs are running, how can I get the actual running time?
2
votes
4answers
358 views

Why is writing so slow on raw device, and so fast on filesystem (USB key)?

I have a USB key that I am trying to benchmark quick'n'dirty on Linux. I'm testing write bandwith. dd on raw partition I created a partition starting at sector 2048, then did a 4 GB sequential ...
5
votes
1answer
163 views

Attempting to Abbreviate kSAR's PDF output

I'm currently writing a cronjob around kSar's command line (non-GUI) options in order generate PDF's. I'm just going to email a PDF of the previous day's activity to a different webmaster (basically ...
3
votes
1answer
345 views

RFC 2544 / Y1564 software implementation

Is there any RFC 2544 and/or Y1564 software available for Linux? I'm aware that tools like iperf, bw-ng and bmon exist, but I was not able to find something that mimics Ethernet tester functionality ...
12
votes
1answer
2k views

Why is my TCP throughput much greater than UDP throughput?

I haven't done anything unusual to my hardware or kernel configurations (all default settings, fresh OS install, Linux kernel 3.11 TCP/IP stack) and I'm averaging about 3.83 million messages per ...
1
vote
1answer
195 views

High performance routing with high churn ruleset. What approach is most likely to scale to C10K and beyond?

I've been asked to create a high throughput router using PC / server hardware. I'm modestly familiar with pf, iptables, and tc, but I've never had such high churn and so many rules. I hope you can ...
23
votes
5answers
3k views

Why is iterating over a file twice faster than reading it into memory and computing twice?

I'm comparing the following tail -n 1000000 stdout.log | grep -c '"success": true' tail -n 1000000 stdout.log | grep -c '"success": false' with the following log=$(tail -n 1000000 stdout.log) echo ...