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  • Cache bandwidth per tick for modern CPUs

    - by osgx
    Hello What is a speed of cache accessing for modern CPUs? How many bytes can be read or written from memory every processor clock tick by Intel P4, Core2, Corei7, AMD? Please, answer with both theoretical (width of ld/sd unit with its throughput in uOPs/tick) and practical numbers (even memcpy speed tests, or STREAM benchmark), if any. PS it is question, related to maximal rate of load/store instructions in assembler. There can be theoretical rate of loading (all Instructions Per Tick are widest loads), but processor can give only part of such, a practical limit of loading.

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  • How to optimize this simple function which translates input bits into words?

    - by psihodelia
    I have written a function which reads an input buffer of bytes and produces an output buffer of words where every word can be either 0x0081 for each ON bit of the input buffer or 0x007F for each OFF bit. The length of the input buffer is given. Both arrays have enough physical place. I also have about 2Kbyte free RAM which I can use for lookup tables or so. Now, I found that this function is my bottleneck in a real time application. It will be called very frequently. Can you please suggest a way how to optimize this function? I see one possibility could be to use only one buffer and do in-place substitution. void inline BitsToWords(int8 *pc_BufIn, int16 *pw_BufOut, int32 BufInLen) { int32 i,j,z=0; for(i=0; i<BufInLen; i++) { for(j=0; j<8; j++, z++) { pw_BufOut[z] = ( ((pc_BufIn[i] >> (7-j))&0x01) == 1? 0x0081: 0x007f ); } } } Please do not offer any compiler specific or CPU/Hardware specific optimization, because it is a multi-platform project.

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  • Visual Studio 2010 - Is it slow for anyone else?

    - by AngryHacker
    I've read a lot of stuff about VS2010 being much more performant than VS2008. When I've finally installed it, I found that it, in fact, is much slower (save for the Add References dialog). For instance, Silverlight projects take twice as long to load, the startup of the IDE itself is much slower, etc... Am I missing something here or is it like this for everyone?

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  • 2k rows update is very slow in MySQL

    - by sergeik
    Hi all, I have 2 tables: 1. news (450k rows) 2. news_tags (3m rows) There are some triggers on news table update which updating listings. This SQL executes too long... UPDATE news SET news_category = some_number WHERE news_id IN (SELECT news_id FROM news_tags WHERE tag_id = some_number); #about 3k rows How can I make it faster? Thanks in advance, S.

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  • Why is Dictionary.First() so slow?

    - by Rotsor
    Not a real question because I already found out the answer, but still interesting thing. I always thought that hash table is the fastest associative container if you hash properly. However, the following code is terribly slow. It executes only about 1 million iterations and takes more than 2 minutes of time on a Core 2 CPU. The code does the following: it maintains the collection todo of items it needs to process. At each iteration it takes an item from this collection (doesn't matter which item), deletes it, processes it if it wasn't processed (possibly adding more items to process), and repeats this until there are no items to process. The culprit seems to be the Dictionary.Keys.First() operation. The question is why is it slow? Stopwatch watch = new Stopwatch(); watch.Start(); HashSet<int> processed = new HashSet<int>(); Dictionary<int, int> todo = new Dictionary<int, int>(); todo.Add(1, 1); int iterations = 0; int limit = 500000; while (todo.Count > 0) { iterations++; var key = todo.Keys.First(); var value = todo[key]; todo.Remove(key); if (!processed.Contains(key)) { processed.Add(key); // process item here if (key < limit) { todo[key + 13] = value + 1; todo[key + 7] = value + 1; } // doesn't matter much how } } Console.WriteLine("Iterations: {0}; Time: {1}.", iterations, watch.Elapsed); This results in: Iterations: 923007; Time: 00:02:09.8414388. Simply changing Dictionary to SortedDictionary yields: Iterations: 499976; Time: 00:00:00.4451514. 300 times faster while having only 2 times less iterations. The same happens in java. Used HashMap instead of Dictionary and keySet().iterator().next() instead of Keys.First().

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  • XNA 2D/3D Drawing method?

    - by Adir
    What would be a better parctice, writing the drawing method inside the GameObject class or in the Game class? GameObject obj = new GameObject(); obj.Draw(); Or GameObject obj = new GameObject(); DrawGameObject(obj);

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  • Database/NoSQL - Lowest latecy way to retreive the following data...

    - by Nickb
    I have a real estate application and a "house" contains the following information: house: - house_id - address - city - state - zip - price - sqft - bedrooms - bathrooms - geo_latitude - geo_longitude I need to perform an EXTREMELY fast (low latency) retrieval of all homes within a geo-coordinate box. Something like the SQL below (if I were to use a database): SELECT * from houses WHERE latitude IS BETWEEN xxx AND yyy AND longitude IS BETWEEN www AND zzz Question: What would be the quickest way for me to store this information so that I can perform the fastest retrieval of data based on latitude & longitude? (e.g. database, NoSQL, memcache, etc)?

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  • Speed up PostGreSQL createdb?

    - by John
    Is there a way to speed up PostgreSQL's createdb command? Normally I wouldn't care, but doing unit testing in Django creates a database every time, and it takes about 5 seconds. I'm using openSUSE 11.2 64-bit, PostgreSQL 8.4.2

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  • Are doubles faster than floats in c#?

    - by Trap
    I'm writing an application which reads large arrays of floats and performs some simple operations with them. I'm using floats because I thought it'd be faster than doubles, but after doing some research I've found that there's some confusion about this topic. Can anyone elaborate on this? Thanks.

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  • how do i do very fast inserts to SQL Server 2008

    - by CharlesO
    I have a project that involves recording data from a device directly into a sql table. I do very little processing in code before writing to sql server (2008 express by the way) typically i use the sqlhelper class's ExecuteNoneQuery method and pass in a stored proc name and list of parameters that the SP expects. This is very convenient, but i need a much faster way of doing this. Thanks.

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  • Create a PHP cache system in MySQL database?

    - by Zach Smith
    I'm creating a web service that often scrapes data from remote web pages. After scraping this data, I have a simple multidimensional array of information to use. The scraping process is fairly taxing on my server, and the page load takes a while. I was considering adding a simple cache system using a MySQL database, where I create one row per remote web page with a the array of information pulled from it stored as a JSON encoded string. Is this a good enough system? Or would something like a text file per web page be a better idea?

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  • require_once at the beginning or when really needed?

    - by takeshin
    Where should I put require_once statements, and why? Always on the beginning of a file, before the class, In the actual method when the file is really needed It depends ? Most frameworks put includes at the beginning and do not care if the file is really needed. Using autoloader is the other case here.

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  • What GC parameters is a JVM running with?

    - by skaffman
    I'm still investigating issues I have with GC tuning (see prior question), which involves lots of reading and experimentation. Sun Java5+ JVMs attempt to automatically select the optimal GC strategy and parameters based on their environment, which is great, but I can't figure out how to query the running JVM to find out what those parameters are. Ideally, I'd like to see what values of the various GC-related -XX options are being used, as selected automatically by the VM. If I had that, I could have a baseline to begin tweaking. Anyone know to recover these values from a running VM?

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  • C#: How to implement a smart cache

    - by Svish
    I have some places where implementing some sort of cache might be useful. For example in cases of doing resource lookups based on custom strings, finding names of properties using reflection, or to have only one PropertyChangedEventArgs per property name. A simple example of the last one: public static class Cache { private static Dictionary<string, PropertyChangedEventArgs> cache; static Cache() { cache = new Dictionary<string, PropertyChangedEventArgs>(); } public static PropertyChangedEventArgs GetPropertyChangedEventArgsa(string propertyName) { if (cache.ContainsKey(propertyName)) return cache[propertyName]; return cache[propertyName] = new PropertyChangedEventArgs(propertyName); } } But, will this work well? For example if we had a whole load of different propertyNames, that would mean we would end up with a huge cache sitting there never being garbage collected or anything. I'm imagining if what is cached are larger values and if the application is a long-running one, this might end up as kind of a problem... or what do you think? How should a good cache be implemented? Is this one good enough for most purposes? Any examples of some nice cache implementations that are not too hard to understand or way too complex to implement?

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  • Looking for a fast hash-function.

    - by Julian
    Hello, I'm looking for a special hash-function. Let's say I have a large list of strings, if I order them by their hash-values they should be ordered quasi randomly. The most important point is: it must be super fast. I've tried md5 and sha1 and they're using to much cpu power. Clashes are not a problem. I'm using javascript, so it shouldn't be too complicated to implement.

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  • Response Time is different for mulitiple execution of the application with the same request Performa

    - by sivananda
    My java application functionality is to provide reference data (basically loads lots of data from xml files into hashmap) and hence we request for one such data from the hashmap based on a id and we have such multiple has map for different set of business data. The problem is that when i tried executing the java application for the same request multiple times, the response times are different like 31ms, 48ms, 72ms, 120ms, 63ms etc. hence there is a considerable gap between the min and max time taken for the execution to complete. Ideally, i would expect the response times to be like, 63ms, 65ms, 61ms, 70ms, 61ms, but in my case the variation of the response time for the same request is varying hugely. I had used a opensource profile to understand if there is any extra execution of the methods or memory leak, but as per my understanding there was no problem. Please let me know what could be the reasons and how can i address this problem.

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  • How to speed up drawing of scaled image? Audio playback chokes during window resize.

    - by Paperflyer
    I am writing an audio player for OSX. One view is a custom view that displays a waveform. The waveform is stored as a instance variable of type NSImage with an NSBitmapImageRep. The view also displays a progress indicator (a thick red line). Therefore, it is updated/redrawn every 30 milliseconds. Since it takes a rather long time to recalculate the image, I do that in a background thread after every window resize and update the displayed image once the new image is ready. In the meantime, the original image is scaled to fit the view like this: // The drawing rectangle is slightly smaller than the view, defined by // the two margins. NSRect drawingRect; drawingRect.origin = NSMakePoint(sideEdgeMarginWidth, topEdgeMarginHeight); drawingRect.size = NSMakeSize([self bounds].size.width-2*sideEdgeMarginWidth, [self bounds].size.height-2*topEdgeMarginHeight); [waveform drawInRect:drawingRect fromRect:NSZeroRect operation:NSCompositeSourceOver fraction:1]; The view makes up the biggest part of the window. During live resize, audio starts choking. Selecting the "big" graphic card on my Macbook Pro makes it less bad, but not by much. CPU utilization is somewhere around 20-40% during live resizes. Instruments suggests that rescaling/redrawing of the image is the problem. Once I stop resizing the window, CPU utilization goes down and audio stops glitching. I already tried to disable image interpolation to speed up the drawing like this: [[NSGraphicsContext currentContext] setImageInterpolation:NSImageInterpolationNone]; That helps, but audio still chokes during live resizes. Do you have an idea how to improve this? The main thing is to prevent the audio from choking.

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  • C# Dictionary Loop Enhancment

    - by Toto
    Hi, I have a dictionary with around 1 milions items. I am constantly looping throw the dictionnary : public void DoAllJobs() { foreach (KeyValuePair<uint, BusinessObject> p in _dictionnary) { if(p.Value.MustDoJob) p.Value.DoJob(); } } The execution is a bit long, around 600 ms, I would like to deacrese it. Here is the contraints : MustDoJob values mostly stay the same beetween two calls to DoAllJobs() 60-70% of the MustDoJob values == false From time to times MustDoJob change for 200 000 pairs. Some p.Value.DoJob() can not be computed at the same time (COM object call) Here, I do not need the key part of the _dictionnary objet but I really do need it somewhere else I wanted to do the following : Parallelizes but I am not sure is going to be effective due to 4. Sorts the dictionnary since 1. and 2. (and stop want I find the first MustDoJob == false) but I am wondering what 3. would result in I did not implement any of the previous ideas since it could be a lot of job and I would like to investigate others options before. So...any ideas ?

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  • why use the "!!!"?

    - by lazyanno
    as follow codes: var a = {}; if(!!!a[tabType]){ a[tabType] = []; a[tabType].push([self,boxObj]); }else{ a[tabType].push([self,boxObj]); } i think !!!a[tabType] equals !a[tabType] why use the "!!!" not "!" ? thank you!

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  • Wpf. Chart optimization. More than million points

    - by Evgeny
    I have custom control - chart with size, for example, 300x300 pixels and more than one million points (maybe less) in it. And its clear that now he works very slowly. I am searching for algoritm which will show only few points with minimal visual difference. I have link to component which have functionallity exactly what i need (2 million points demo): http://www.mindscape.co.nz/demo/SilverlightElements/demopage.html#/ChartOverviewPage I will be grateful for any matherials, links or thoughts how to realize such functionallity.

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