Berkeley CSUA MOTD:Entry 45019
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2025/07/08 [General] UID:1000 Activity:popular
7/8     

2006/10/27-11/1 [Computer/SW/OS/VM, Computer/HW/CPU] UID:45019 Activity:nil
10/30   Can a hyper-threading CPU run two threads in two separate apps at the
        same time?  How does it handle the two different virtual memory
        mapping?  If I mostly run processes where only one thread is active,
        (e.g. compilation, SETI@home in background, VirtualPC or VMware
        instances), does hyper-threading help or hurt performance?  (I know I
        really should profile to find out, but I want to know the theoretical
        answer.)  Thx.
        \_ They get interleaved the same as anything else.  Go look up Intel's
           *very* well written white papers on the topic.  You won't find
           better answers anywhere else.
        \_ Intel has published several white papers on their site that explain
           in easily read English exactly how HT works.  You are unlikely to
           find a better explanation anywhere else.  Kudos to their doc
           writers on that one.
        \_ Virtual memory is not an issue.  As to the rest, unless you are
           doing stuff where getting about 1 percent more out of your cpu
           matters, don't worry about it.  Hyperthreading has a bit of
           performance hit in most cases but makes up for it by making
           the computer much more responsive at high load.  In a gui environment
           this makes you computer feel zippier and is worth the performance
           cost.
           \_ Actually, it makes the computer less responsive under a high
              load. Why? Because the CPU is trying to execute more
              processes than it has processors. Try this experiment: Run
              three jobs with a nice level of 20. Then run one interactive
              job. See how (un)responsive it is? Now turn off HT and
              repeat the experiment. I guarantee you it will be more
              responsive in the latter case.
2025/07/08 [General] UID:1000 Activity:popular
7/8     

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