Date: Wed, 15 Aug 2012 14:40:06 +0400 From: Lev Serebryakov <lev@FreeBSD.org> To: Alexander Motin <mav@FreeBSD.org> Cc: Adrian Chadd <adrian@freebsd.org>, Doug Barton <dougb@FreeBSD.org>, current@freebsd.org Subject: Re: CURRENT as gateway on not-so-fast hardware: where is a bottlneck? Message-ID: <1849591745.20120815144006@serebryakov.spb.ru> In-Reply-To: <502B775D.7000101@FreeBSD.org> References: <157941699.20120815004542@serebryakov.spb.ru> <CAJ-Vmon86-FPs4%2BXXkQXAow1jW465pMM2Sj7ZHi_0_E9VYSFSA@mail.gmail.com> <502AE8B5.9090106@FreeBSD.org> <502B775D.7000101@FreeBSD.org>
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Hello, Alexander. You wrote 15 =E0=E2=E3=F3=F1=F2=E0 2012 =E3., 14:18:05: AM> It is quite pointless to speculate without real info like mentioned AM> above KTR_SCHED traces. Main thing I've learned about schedulers, things AM> there never work as you expect. There are two many factors are relations AM> to predict behavior in every case. I'll take these with as much variants (ULE and 4BSD, polling with HZ=3D1000 and interrupts with default HZ) as I can, in day or two. Now I have kernels with KTR compiled in (GEN, NET and SCHED). AM> About Soekris and idle CPU measurement, let's start from what kind of= =20 AM> eventtimer is used there. As soon as it is UP machine, I guess it uses AM> i8254 timer in periodic mode. It means that it by definition can't It doesn't have any other timers. You could think about this machine as about good old "true" i386, with PCI (and some additional fancy commands in CPU core, something like classic Pentium) but nothing more. kern.eventtimer.choice: i8254(100) RTC(0) kern.eventtimer.et.RTC.flags: 17 kern.eventtimer.et.RTC.frequency: 32768 kern.eventtimer.et.RTC.quality: 0 kern.eventtimer.et.i8254.flags: 1 kern.eventtimer.et.i8254.frequency: 1193182 kern.eventtimer.et.i8254.quality: 100 kern.eventtimer.periodic: 1 kern.eventtimer.timer: i8254 kern.eventtimer.activetick: 1 kern.eventtimer.idletick: 0 kern.eventtimer.singlemul: 2 AM> properly measure load from treads running from hardclock, such as=20 AM> dummynet, polling netisr threads, etc. You see, here are two different problems: (a) with polling, system is responsive under any load, but wire2wifi performance is hugely affected by wire2wire traffic (and mpd5 inbetween). And, yes, "top" seems to lie about idle time. (b) with interrupts, system works much better when it works (wire2wifi speed is affected by wire2wire traffic, but to much less extent), but it freezes every third minute for minute, when traffic is passed, but no user-level applications including BIND and DHCP server) works at all FOR MINUTE OR MORE. It not looks like 100ms lag, which could affect video playback. It looks like 60-120 seconds lag! At least, in case of ULE, I didn't try 4BSD yet. --=20 // Black Lion AKA Lev Serebryakov <lev@FreeBSD.org>
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