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The Problem It is common for students to have portability problems with their scripts when they do their initial development on systems that use bash, for example, as /bin/sh. While bash supports all functionality in the POSIX standard, it also supports a wide range of extended functionality that is not defined by POSIX. When a script is written to use such ...


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You need more data; if you're having high %iowait you need to find out what is causing it. To do this you can use the following tools: iotop especially with -a. atop -d 1 sar is a great tool for historical logging; but you need to use a real-time tool for monitoring it. I made a pretty detailed post about doing this here: ...


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You need to add the -c option to do more than 64 blocks and probabky -b to specify a block size other than 1KiB. Right now you're doing 64KiB at a time, which is a lot of seeks. Something like: badblocks -c 2560 -b 4096 -wsv -t random /dev/«device» ought to run much faster. That's 10MiB (= 4KiB × 2560) at a time; go higher with -c if that's still not ...


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The answer (as I now know): concurrency. In short: My sequential write, either using dd or when copying a file (like... in daily use), becomes a pseudo-random write (bad) because four threads are working concurrently on writing the encrypted data to the block device after concurrent encryption (good). Mitigation (for "older" kernels) The negative effect ...


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First off, you're confused about what some of those are. You can set the physical extent size with a fair bit of flexibility (vgreate's -s). But it doesn't matter, you should just go with the default. To quote the manpage: The default is 4 MiB.… [H]aving a large number of extents will slow down the tools but have no impact on I/O performance to the ...


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It may be that at any specific time only one of the two cores is saturated, but on average it looks like they are both at about 50% (because kernel randomly assigns a single-threaded IPsec process to both cores; however as far as I have noticed Linux (unlike Windows) usually tries to keep a thread on the same core). At some short periods IPSec may wait also ...


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Having it installed does not really slow it down. It does use some memory and diskspace though. However, what are you planning to do with it? running a browser would slow down your server. When there are no active programs in the desktop environment it doesn't have a noticeable impact. I used to install a desktop environment for some clients so their ...


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Just having GDM running (i.e., when no desktop session is started) shouldn't have much of an impact. It will eat some memory, which will eventually be swapped off if needed, but I doubt it will have an impact on CPU or disk I/O when idle. You might also run a lighter DM or none at all. But yes, it can be turned on and off as needed, in which case it will ...


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Installing it... no. Running it at the same time, making the desktop environment and the other application compete for resources (CPU time, memory, IO, etc.), then the answer is yes. The more applications you have running competing for resources, any or both of them will slow down.


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I am wondering if it is because artificial waits or sleeps have been inserted into the crypto. It's not very likely imo, but... http://www.tau.ac.il/~tromer/acoustic/ Couldn't post this as a comment, would have been a better fit that way.


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Monitor the trends over time and look for anomalies. The "normal" values differ depending on the type of application load and in turn, what the application does on a regular basis.


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top is the best tool I know to find what process is using the system ressources. on my machine : $ top top - 14:14:00 up 1 day, 2:00, 4 users, load average: 0.24, 0.23, 0.24 Tasks: 235 total, 3 running, 232 sleeping, 0 stopped, 0 zombie %Cpu(s): 3.2 us, 0.5 sy, 0.0 ni, 96.2 id, 0.1 wa, 0.0 hi, 0.0 si, 0.0 st KiB Mem: 7870416 total, ...


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Usually load average is because of lots of things wanting CPU, but not always. A common culprit is a process waiting for IO - disk or network. Try running ps -e v and looking for process state flags. state The state is given by a sequence of characters, for example, "RWNA". The first character indicates the run state of the process: D Marks a ...



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