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Power regression by futex problem?

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  • Power regression by futex problem?

    Hello everybody,

    I've started playing with MySQL vs. MariaDB lately. The replacement works just fine, though I have some concerns about a power regression (and possibly more side effects). This does not only effect MySQL/MariaDB but every threaded application using fast user-space locking.

    Tracing system calls of these processes with strace I can see a futex timeout every second. Searching for this behavior on Google brings up a lot of discussions about 2012's leap second, though MySQL and others are reported to generate really high load. As said for me this is just one wakeup a seconds.

    Setting the time with 'date -s "$(date)"' does not help in my case. Setting the time back for X seconds makes the futex problem disappear for these X seconds. After that it just continues.

    As a lot of applications are threaded these days and every running threaded process seems to wake the system each second this looks like a really bad power regression to me. I could reproduce this with Arch Linux and openSUSE, have not tested any more.

    Any clue what is going on?