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• KVM guest disk performance

  - by Alex

  My KVM guest does max. 200MB/s although the host does easily 700MB/s (Raid 0 with 4 SSDs). Configuration: File-based storage (raw), cache none. Host 24 cores, 96GB ram, Ubuntu 12.04.1 LTS and virt-manager. I suspect the CPU to be the bottleneck (one core goes up during hdparm). Anyone experienced the same or has an explanation ? Edit: one more info: guest is the same as host (Ubuntu 12). Same poor disk performance observed with Windows 2008 R2 and Suse Enterprise Linux (9 or 10 I think). Max 1 guest running.

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• is there a bug with restart in edubuntu 12.04

  - by Ket

  After a clean install of edubuntu 12.04 on an Acer AO531-h netbook, restart doesn't work. The process starts normally but just before it shuts down the netbook freezes and I have to force shut down. The command "sudo reboot" has the same problem. I have no issues with shut down, only with restart. I'm absolute beginner. Netbook specs: Acer, intel atom CPU N270 @1.60GHz, 1.05 GHz 0.98GB RAM Dual booting with windows xp. No problems with windows.

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• How to make bash script run with a latency (i.e. wait 1 sec at each iterations)?

  - by user2413

  I have this bash script; for (( i = 1 ; i <= 160 ; i++ )); do qsub myccomputations"${i}".pbs done Basically, I would prefer if there was a 1 second delay between each iteration. The reason is that at each iterations, it sends the program file mycomputation"${i}$.pbs to a core node for solving. Solving in this instance involves the use of pseudo random numbers. I suspect the RNG I use (R's) uses CPU time as seed because as things are now I get repeating pseudo random numbers (at the rate of approx 1 out of 100). So how to you ask bash to for (( i = 1 ; i <= 160 ; i++ )); do wait 1 sec qsub myccomputations"${i}".pbs done

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• Question about Partitioning

  - by Trent C

  I am looking to dual boot Windows 7 and Ubuntu 13.10. I have been using windows for work and school for over a year, and have about 100 gig of stored files (backed up of course) and some paid programs. Because of this, I really want my partitioning experience to go well. Unfortunately, I am running into a bit of an anomoly When I load GPart, I see that my sda drive is unallocated http://i.imgur.com/Hi2XhIr.png Whereas my sdb appears to contain all of the windows files and partitions, and make up my C: drive http://i.imgur.com/aaCOXje.png Is this going to be an issue, as all literature on dual boot installation references sda? How do I work around it? System Info: Lenovo IdeaPad Y570- 750GB HDD with 64GB SSD Processor: Intel® Core™ i7-2670QM CPU @ 2.20GHz × 8

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• Performance triage

  - by Dave

  Folks often ask me how to approach a suspected performance issue. My personal strategy is informed by the fact that I work on concurrency issues. (When you have a hammer everything looks like a nail, but I'll try to keep this general). A good starting point is to ask yourself if the observed performance matches your expectations. Expectations might be derived from known system performance limits, prototypes, and other software or environments that are comparable to your particular system-under-test. Some simple comparisons and microbenchmarks can be useful at this stage. It's also useful to write some very simple programs to validate some of the reported or expected system limits. Can that disk controller really tolerate and sustain 500 reads per second? To reduce the number of confounding factors it's better to try to answer that question with a very simple targeted program. And finally, nothing beats having familiarity with the technologies that underlying your particular layer. On the topic of confounding factors, as our technology stacks become deeper and less transparent, we often find our own technology working against us in some unexpected way to choke performance rather than simply running into some fundamental system limit. A good example is the warm-up time needed by just-in-time compilers in Java Virtual Machines. I won't delve too far into that particular hole except to say that it's rare to find good benchmarks and methodology for java code. Another example is power management on x86. Power management is great, but it can take a while for the CPUs to throttle up from low(er) frequencies to full throttle. And while I love "turbo" mode, it makes benchmarking applications with multiple threads a chore as you have to remember to turn it off and then back on otherwise short single-threaded runs may look abnormally fast compared to runs with higher thread counts. In general for performance characterization I disable turbo mode and fix the power governor at "performance" state. Another source of complexity is the scheduler, which I've discussed in prior blog entries. Lets say I have a running application and I want to better understand its behavior and performance. We'll presume it's warmed up, is under load, and is an execution mode representative of what we think the norm would be. It should be in steady-state, if a steady-state mode even exists. On Solaris the very first thing I'll do is take a set of "pstack" samples. Pstack briefly stops the process and walks each of the stacks, reporting symbolic information (if available) for each frame. For Java, pstack has been augmented to understand java frames, and even report inlining. A few pstack samples can provide powerful insight into what's actually going on inside the program. You'll be able to see calling patterns, which threads are blocked on what system calls or synchronization constructs, memory allocation, etc. If your code is CPU-bound then you'll get a good sense where the cycles are being spent. (I should caution that normal C/C++ inlining can diffuse an otherwise "hot" method into other methods. This is a rare instance where pstack sampling might not immediately point to the key problem). At this point you'll need to reconcile what you're seeing with pstack and your mental model of what you think the program should be doing. They're often rather different. And generally if there's a key performance issue, you'll spot it with a moderate number of samples. I'll also use OS-level observability tools to lock for the existence of bottlenecks where threads contend for locks; other situations where threads are blocked; and the distribution of threads over the system. On Solaris some good tools are mpstat and too a lesser degree, vmstat. Try running "mpstat -a 5" in one window while the application program runs concurrently. One key measure is the voluntary context switch rate "vctx" or "csw" which reflects threads descheduling themselves. It's also good to look at the user; system; and idle CPU percentages. This can give a broad but useful understanding if your threads are mostly parked or mostly running. For instance if your program makes heavy use of malloc/free, then it might be the case you're contending on the central malloc lock in the default allocator. In that case you'd see malloc calling lock in the stack traces, observe a high csw/vctx rate as threads block for the malloc lock, and your "usr" time would be less than expected. Solaris dtrace is a wonderful and invaluable performance tool as well, but in a sense you have to frame and articulate a meaningful and specific question to get a useful answer, so I tend not to use it for first-order screening of problems. It's also most effective for OS and software-level performance issues as opposed to HW-level issues. For that reason I recommend mpstat & pstack as my the 1st step in performance triage. If some other OS-level issue is evident then it's good to switch to dtrace to drill more deeply into the problem. Only after I've ruled out OS-level issues do I switch to using hardware performance counters to look for architectural impediments.

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• Dimming the backlight is irreversible on a Samsung Q210 notebook, what do I do?

  - by user27304

  I'm new to the community, although I have been using Ubuntu since 2010. I have a Samsung Q210 notebook; Specs: Intel® Core™2 Duo CPU P8400 @ 2.26GHz × 2 4 Gigs RAM Nvidia 9200m GS (although system information in Ubuntu doesn't know) 194 GB HD OS: Ubuntu 11.10 Kernel is 3.0.0-12-generic-pae Although Samsung seems to be infamous for problems with Ubuntu, after upgrading to Oneiric, finally the FN Brightness Buttons are recognized. The only problem is, after dimming the backlight for a fixed amount of steps (3 or 4, I dare not count now because that would mean rebooting because I can't see anything), the display goes completely dark and using the FN buttons to brighten the backlight does not work anymore (before reaching that threshold, going brighter after dimming works). Now what do I do? File a bug report? If not, what then? If yes, how? Not sure... guess I should ask here first.. thanks for answering in advance.

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• Fan very loud in Ubuntu 12.10

  - by Jon

  I recently installed 12.10 on my Desktop PC, moving away from Windows 7. For some reason, the fan in my computer is making an enormous amount of noise (it is running at full speed constantly). Under Windows 7, the fan would slow itself down and run at an acceptable noise level. Now, it is nearly unbearable. Checked the processes, and none are taking up a huge load on the CPU. Please help as I really can't endure this noise, and I do not want to go back to Windows 7 on this box. Some specs: - Intel 2.26 duo core - ATI 4870 - 4GB - 650W power supply

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• Does the latest version of Ubuntu (12.04) support Unity 3D?

  - by Douglas Combs

  I just installed the latest version of Ubuntu (12.04) 64bit. I am using a Radeon HD 7750 vid card. I think I have the Catalyst driver installed correctly. But when I go to system and look at the details, it shows that my graphics is VESA:01. Does this mean I it, I didn't correctly install my driver? System Specs: MB: ASUS P7P55-M CPU: Intel i5 Quad Core MEM: 4GB DD3 VC: HIS Radeon HD 7750 (1GB DDR5) Thanks for help.

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• Can the JVM recover from an OutOfMemoryError without a restart

  - by askullhead

  Can the JVM recover from an OutOfMemoryError without a restart if it gets a chance to run the GC before more object allocation requests come in? Do the various JVM implementations differ in this aspect? EDIT: My question was about the JVM recovering and not the user program trying to recover by catching the error. In other words if an OOME is thrown in an application server (jboss/websphere/..) do I have to restart it? Or can I let it run if further requests seem to work without a problem. Sorry if that wan't clear.

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• Strange profiling results: definitely non-bottleneck method pops up

  - by jkff

  I'm profiling a program using sampling profiling in YourKit and JProfiler, and also "manually" (I launch it and press Ctrl-Break several times to get thread dumps). All three methods give me extremely strange results: some tens of percents of time spent in a 3-line method that does not even do any allocation or synchronization and doesn't have loops etc. Moreover, after I made this method into a NOP and even removed its invocation completely, the observable program performance didn't change at all (although it got a negligible memory leak, since it was a method for freeing a cheap resource). I'm thinking that this might be because of the constraints that JVM puts on the moments at which a thread's stacktrace may be taken, and it somehow turns out that in my program it is exactly the moments where this method is invoked, although there is absolutely nothing special about it or the context in which it is invoked. What can be the explanation for this phenomenon? What are the aforementioned constraints? What further measurements can I take to clarify the situation?

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• How to implement arrays in an interpreter?

  - by Ray

  I have managed to write several interpreters including Tokenizing Parsing, including more complicated expressions such as ((x+y)*z)/2 Building bytecode from syntax trees Actual bytecode execution What I didn't manage: Implementation of dictionaries/lists/arrays. I always got stuck with getting multiple values into one variable. My value structure (used for all values passed around, including variables) looks like this, for example: class Value { public: ValueType type; int integerValue; string stringValue; } Works fine with integers and strings, but how could I implement arrays? (From now on with array I mean arrays in my experimental language, not in C++) How can I fit the array concept into the Value class above? Is it possible? How should I make arrays able to be passed around just as you could pass around integers and strings in my language, using the class above? Accessing array elements or memory allocation wouldn't be the problem, I just don't know how to store them.

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• Firefox 4 : sortie de la beta 12, améliorations du support du Flash et de l'accélération matérielle

  Firefox 4 : sortie de la beta 12 Améliorations du support du Flash et de l'accélération matérielle Mise à jour du 28/02/11 La douzième ? et a priori dernière - beta de Firefox 4 est sortie ce week-end. Elle corrige 7.000 bugs et apporte une amélioration dans la lecture des vidéos (en Flash). L'intégration de l'accélération matérielle (allouer des tâches spécifiques de calcul au GPU plutôt qu'au CPU) a elle aussi été retravaillée. Le tout permettant une meilleure stabilité du navigateur. Elle n'inclut malheureusement pas encore les patchs « miracles*» qui permettent de diviser par deux son temps de démarrage (lire par ail...

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• Redoundant code in exception handling

  - by Nicola Leoni

  Hi, I've a recurrent problem, I don't find an elegant solution to avoid the resource cleaning code duplication: resource allocation: try { f() } catch (...) { resource cleaning code; throw; } resource cleaning code; return rc; So, I know I can do a temporary class with cleaning up destructor, but I don't really like it because it breaks the code flow and I need to give the class the reference to the all stack vars to cleanup, the same problem with a function, and I don't figure out how does not exists an elegant solution to this recurring problem.

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• Parallel.For Inconsistency results

  - by ni Gue ???

  I am using VB.net to write a parallel based code. I use Parallel.For to generate pairs of 500 objects or in combination C(500,2) such as the following code; but I found that it didn't always generate all combinations which should be 124750 (shown from variable Counter). No other thread was runing when this code was run. I am using a Win-7 32 Bit desktop with Intel Core i5 CPU [email protected], 3.33 GHz and RAM 2GB. What's wrong with the code and how to solve this problem? Thank You. Dim Counter As Integer = 0 Parallel.For(0, 499, Sub(i) For j As Integer = i + 1 To 499 Counter += 1 Console.Write(i & ":" & j) Next End Sub) Console.Writeline("Iteration number: " & Counter)

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• pwmconfig: "There are no pwm-capable sensor modules installed"

  - by Sman789

  I'm trying to reduce my fan speed with fancontrol and pwmanager because, despite the temperatures being the same, they are much louder on Linux (Ubuntu Gnome 14.04) than on Windows. I've followed the instructions in the first answer here but when running pwmanager I get pwmconfig: "There are no pwm-capable sensor modules installed" I know that my system has working thermal sensors because PSensor has no trouble telling me my CPU temp and GPU temp. I would appreciate any help you can give in helping me reduce my fan speed to that of Windows (which uses the ASUS AI Suite 3 software which came with the Z87-A motherboard, if that's relevant).

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• Design a Distributed System

  - by Bonton255

  I am preparing for an interview on Distributed Systems. I have gone through a lot of text and understand the basics of the area. However, I need some examples of discussions on designing a distributed system given a scenario. For example, if I were to design a distributed system to calculate if a number N is primary or not, what will the be design of the system, what will be the impact of network latency, CPU performance, node failure, addition of nodes, time synchronization etc. If you guys could present your in-depth thoughts on this example, or point me to some similar discussion, that would be really helpful.

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• Clock drift even though NTPD running

  - by droffo

  I'm having a problem with the clock drifting on my PC. I'M running Ubuntu 10.10 on an somewhat crusty IBM e-server (1.5GB RAM, 2.4GHz CPU) ntpd is running (started at run level 2) servers are defined: server 1.us.pool.ntp.org server 2.us.pool.ntp.org server 3.us.pool.ntp.org server time.nrc.ca server ntp1.cmc.ec.gc.ca server ntp2.cmc.ec.gc.ca server wuarchive.wustl.edu server clock.psu.edu Looking at the log file, it would seem that the ntp daemon is running, but the system clock never seems to be set, however. If I manually set the time from a Casio "atomic" watch, the date/time displayed by the Clock applet drifts out of sync over time. Looking at the log file (below) it would seem the ntp daemon started ok and is running. So I am totally flummoxed right now :-( Here's a copy of my ntp.log file.

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• Uncontrolled Fan and Crash

  - by RobotbeatsHuman

  I don't have sensors to properly run lm-sensors. The computer will turn on but shortly there after all the fans in it will speed way up. It stays like this for a few minutes and then the computer shuts off. Tried resetting the BIO. Went to try installing a BIOs update but it wont stay on long enough for me to try that or to do a clean install. Could this be the motherboard dying? It's mainly the CPU fan that ends up going max. after a few minutes. I checked the PSU and It's a Dell Inspiron 580. If you need more system specs just le me know.

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• Using Interlocked.Exchange(ref Enum, 1) to prevent re-entrancy [migrated]

  - by makerofthings7

  What options do I have for pending work that can't acquire a lock via the following sample? System.Threading.Interlocked.CompareExchange<TrustPointStatusEnum> (ref tp.TrustPointStatus, TrustPointStatusEnum.NotInitalized,TrustPointStatusEnum.Loading); Based on my research think I have the following options: I can use Threading.SpinWait (for very quick IO tasks) at the cost of CPU I can use Sleep() which has an unreliable wake up time I'm not sure of any other option, but what I want to make sure of is that all these options work with the .NET 4 async and await keywords, especially if I use Task to run them on a background thread

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• Microsoft Developers Development Laptops [closed]

  - by FidEliO

  Possible Duplicate: What should I be focusing on when building a development PC? I am a Microsoft Developer on Sharepoint and ASP.NET. I am tring to buy a new laptop since the one that I have is an old one. From my point of view, Microsoft Development tools are becomming more and more resource-consuming (I don't find a suitable reason for it though). So I thought I would go for a Lenovo U260 i-7. I do not know exactly if it is going to meet my requirement so that is why I wanted to ask specifically Microsoft Developers about the specification of CPU, RAM, and Storage Disk. Thanks in advance

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• Blank Processes (?) in Natty Narwhal

  - by A Hylian Human

  I've noticed that there a seemingly blank processes (no process name, no cmdline info, only an ID), which also appear to cause my CPU to be running like crazy. My fans are going pretty much full speed and I have no idea what to do. Restarting does not help. Whenever I try to kill the process IDs, nothing happens. It's like new blank processes are continuously being created. I am really surprised that I am able to write up this question without Firefox lagging like crazy (and trust me, it's not Firefox causing the issue, as far as I can tell).

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• Loud fans despite cool system under Linux (but not Windows)

  - by Sman789

  My new desktop computer runs almost silently under Windows, but the fans seem to run on a constantly high setting under Linux. Psensor shows that the GPU (with NVidia drivers) is thirty-something degrees and the CPU is about the same, so it's not just down to Linux somehow being more processor-intensive. I've read that the BIOS controls the fans under Linux, which makes sense given the high fan speeds when in BIOS as well. It's under Windows, when the ASUS AI Suite 3 software seems to take control, that the system runs more quietly and only speeds the fans up when required. So is there a Linux app which offers a similar dynamic control of the fans, or a setting hidden somewhere in the ASUS BIOS which allows the same but regardless of the OS? EDIT - I've tried using lm-sensors and fancontrol, but pwmconfig tells me "There are no pwm-capable sensor modules installed". This is after the sensors-detect command does find an 'Intel digital thermal sensor', and despite the sensors working fine in apps like psensor. Help getting this to work would likely solve the problem.

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• Ikoula propose 1000 nouveaux serveurs virtuels dédiés Flex'Servers gratuits pendant un mois à l'occasion des TechDays

  Ikoula propose 1000 nouveaux serveurs virtuels dédiés Flex'Servers gratuits Pendant un mois à l'occasion des TechDays Ikoula avait déjà lancé une promotion sur son offre Flex'Server en proposant 500 seveurs gratuits. Aujourd'hui, l'entreprise renouvelle son opération à l'occasion des TechDays et relance son offre. Elle comprend désormais de nouvelles ressources à prix privilégié. Quatre configurations sont disponibles : de ½ à 4 CPU, de 256 Mo à 2 Go de RAM, et de 10 à 80 Go de disque dur. A l'occasion des TechDays, 1 000 Flex'Servers sont offerts pendant un mois. Après le premier mois, ces serveurs dédiés virtuels sont facturés à partir de 5.99€ HT/moi...

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• How can I make KDE faster in Ubuntu 12.04. It's very slow

  - by Rizwan Rifan

  I installed the kubuntu-desktop package in Ubuntu 12.04 LTS, but the problem is KDE responses very slowly. If I click on an application's icon to run it, it appears after 10 seconds and sometimes does not appear at all. It hangs all the time. The cursor is almost impossible to follow because of the lag. I have read on the Internet that Unity uses more memory and CPU than KDE. But on my PC Unity runs smoothly and KDE does not. So what should I do to make KDE as fast, responsive and smooth as Unity? My specifications are as follows: RAM: 1.5 GB (DDR2) Processor: 3 GHz Dual Core Graphics Card: Intel HD graphics with 256 MB memory.

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• Java is very slow on my laptop

  - by Ryan McClure

  I have 1.6.0_30 JRE on my 11.10 install. I have 3 GB of RAM and an Intel Core2 Duo CPU T6600 @ 2.20GHz × 2. Whenever I use my Java to play a game, the Java runs at about 4-5 FPS. When I used Windows, I found that I could get around 40 FPS. I'm not too terribly worried about this, but are there settings that I can tweak that I don't know about? If not, why is it that JRE Java can't do as much on Ubuntu as it can on Windows? Also, this may be related but I'm not too sure--My fan runs very fast when running a Java application. Is there a correlation?

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