Date: Sat, 6 Jun 1998 21:11:58 +1000 From: Bruce Evans <bde@zeta.org.au> To: bde@zeta.org.au, current@FreeBSD.ORG, straka@home.com Subject: Re: strange behavior with signal latencies Message-ID: <199806061111.VAA10115@godzilla.zeta.org.au>
next in thread | raw e-mail | index | archive | help
>BTW, these latancy times really go out the window (10+ms ) when >the system is loaded with disk writing or network activity. I have performed >similar tests on an Ultra 30 box running Solaris 2.6. Even under extreme >loading, the latencies stay below 1ms (its no VxWorks, but it ain't bad for >soft >realtime). It appears that Solaris does very little work in hardware >interrupts, >defering work to preemtable kernel threads which are under control of the >scheduler. They offer a realtime scheduling class which has higher priority >than their system scheduling class. The amount of work we currently do in >FreeBSD in hardware and software interrupts coupled with the >non-preemtable nature of kernel activity precludes us from doing even >soft realtime work. Even software interrupts can be masked for several clock ticks if the system is overloaded. It is easy to overload systems using silly hardware configurations. E.g., take any modern IDE drive with a throughput of 9MB connected to an old PIO1 interface with a throughput of 3MB. Then writing a 1MB will take at least 1/3 second entirely in the kernel, and if the kernel manages to queue 1MB of buffers, accessing them will take at least 1/3 second entirely in h/w interrupt handlers (unless the disk has to seek). Fix: don't use silly hardware configurations :-). Bruce To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?199806061111.VAA10115>