Date: Sat, 17 Jul 2010 22:34:36 +0300 From: Alexander Motin <mav@FreeBSD.org> To: "Jayachandran C." <c.jayachandran@gmail.com> Cc: Neel Natu <neel@freebsd.org>, freebsd-mips@freebsd.org Subject: Re: [RFC] Event timers on MIPS Message-ID: <4C4205CC.6080700@FreeBSD.org> In-Reply-To: <AANLkTik8_NGm7nKYXT1d1E4Vj6vYQPWHnnLDi78YnvQD@mail.gmail.com> References: <4C41A248.8090605@FreeBSD.org> <AANLkTilKYw4UqmfEee9zHGosEDzy4hiFob1d8R9jcB25@mail.gmail.com> <4C41B4CF.6080409@FreeBSD.org> <AANLkTik8_NGm7nKYXT1d1E4Vj6vYQPWHnnLDi78YnvQD@mail.gmail.com>
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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. We also have a > PIC which can provide a better timestamp and timer interrupts. This > PIC timestamp can be read from all CPUs but the timer interrupt can be > delivered to just one CPU at a time. I think this is how we ended up > with the current implementation, but any suggestions on how to improve > this is welcome. I would prefer to not mix the things. I think: - PIC timestamp looks like the best candidate for system timecounter. - per-CPU counters could be registered as per-CPU timecounters with set_cputicker() - the main criteria there is a speed. - 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. - 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. - if there is any other timer hardware - it also should be registered - it will give additional flexibility. PS: I've managed to run MALTA kernel with patch under gxemul. It works, except time is not going right. But I suppose it is emulator problem, as original kernel works the same. -- Alexander Motin
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