Date: Tue, 27 Jul 2010 14:54:09 +0530 From: "Jayachandran C." <c.jayachandran@gmail.com> To: Alexander Motin <mav@freebsd.org> Cc: Randall Stewart <rrs@freebsd.org>, Neel Natu <neel@freebsd.org>, freebsd-mips@freebsd.org Subject: Re: [RFC] Event timers on MIPS Message-ID: <AANLkTikUpqLeogkqxqWzzejp=7FstHX2wVRWNrYoWGCp@mail.gmail.com> In-Reply-To: <4C4205CC.6080700@FreeBSD.org> References: <4C41A248.8090605@FreeBSD.org> <AANLkTilKYw4UqmfEee9zHGosEDzy4hiFob1d8R9jcB25@mail.gmail.com> <4C41B4CF.6080409@FreeBSD.org> <AANLkTik8_NGm7nKYXT1d1E4Vj6vYQPWHnnLDi78YnvQD@mail.gmail.com> <4C4205CC.6080700@FreeBSD.org>
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On Sun, Jul 18, 2010 at 1:04 AM, Alexander Motin <mav@freebsd.org> wrote: > Jayachandran C. wrote: >> On XLR we would like to use the count/compare which is faster but less >> accurate on all cpus - we can have upto 32 cpus now. =A0We also have a >> PIC which can provide a better timestamp and timer interrupts. =A0This >> PIC timestamp can be read from all CPUs but the timer interrupt can be >> delivered to just one CPU at a time. =A0I think this is how we ended up >> with the current implementation, but any suggestions on how to improve >> this is welcome. As a first step, I have copied the count /compare code from mips with minor modifications into mips/rmi, this lets me boot up (checked in as r210528). I would like to add the PIC based clock next. > I would prefer to not mix the things. > > I think: > =A0- PIC timestamp looks like the best candidate for system timecounter. > =A0- per-CPU counters could be registered as per-CPU timecounters with > set_cputicker() - the main criteria there is a speed. > =A0- if per-CPU counters are synchronized between CPUs - they could be > registered as alternative timecounter for people who wish fastest > timecounting; if they are not - they are useless in that role. > =A0- both PIC timer and per-CPU comparators should be independently > registered as eventtimers - it is better to have two of them to from > accounting correctness PoV, and it will allow user to experiment which > one he likes more. > =A0- if there is any other timer hardware - it also should be registered = - > it will give additional flexibility. The per-cpu count/compare counters are not synchronized on XLR. So your suggestion would be to add a PIC based clock which calls tc_init() and et_register(), and to leave the set_cputicker() to be the count/compare? Also, with just the count/compare, I get these print on early mutiuser boot= up. --- calcru: runtime went backwards from 85936878 usec to 236488 usec for pid 1286 (rpcbind) calcru: runtime went backwards from 7158742 usec to 19700 usec for pid 1285 (nfsiod 0) calcru: runtime went backwards from 111005442 usec to 305474 usec for pid 1257 (syslogd) calcru: runtime went backwards from 10740196 usec to 29555 usec for pid 1048 (devd) -- Did not get much time to investigate, any idea what the cause can be? Thanks, JC.
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