Hi Omer, On Sat, May 7, 2011 at 3:29 PM, Omer Zak <w...@zak.co.il> wrote: > I have a PC with powerful processor, lots of RAM and SATA hard disk. > Nevertheless I noticed that sometimes applications (evolution E-mail > software and Firefox[iceweasel] Web browser) have the sluggish feel of a > busy system (command line response time remains crisp, however, because > the processor is 4x2 core one [4 cores, each multithreads as 2]). > > I run the gnome-system-monitor all the time. > > I notice that even when those applications feel sluggish, only one or at > most two CPUs have high utilization, and there is plenty of free RAM (no > swap space is used at all). >
The phenomena you are describing could be (though other explanations are still possible) a result of a completely different issue: Having 4 cores with 2 virtual cores on each means 8 threads could, theoretically, run in parallel. However, there is a large number of factors preventing 4 cores CPU from being 4 times faster than a single core CPU. The most common are, as of time being, the applications themselves - many of them are not written in a manner which enables them to use more than 1 CPU. Usually, it is either due to doing all of the CPU intensive work in one thread (i.e. the thread which renders the webpages to the screen in iceweasel) or due to coarse grain locking (i.e. locking the entire mozilla application every time we do garbage collection on the java-script heap, etc.). There are also issues of resource contention (i.e. firefox has a big working set, and therefore its speed is more affected by the amount of time it takes to access the RAM than it is affected by the CPU power - the CPU tends to mostly wait for data to arrive from the RAM), but that is less likely the case according to your description. When large amount of RAM is available, the chances that the sluggishness is due to slow disk access are rather slow - Linux is very aggressive about keeping everything in the cache, and if your application was spending most of its time waiting for disk I/O, you wouldn't have seen large CPU usage percentages - it was going into a "sleep" state until the data arrives, and wouldn't affect the user CPU usage percentage. To verify that, run top while the application is sluggish, and check if it the CPU usage is mostly in the user code (pressing "1" while top is running will show the per-CPU statistics in the top half of the screen, the percentage next to "us" is the relative amount of time the CPU spent running user code since the last sample). Good luck in hunting down your slowness. --Shachar _______________________________________________ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
