Messages in this thread | | | Date | Tue, 25 Jul 2006 14:28:33 -0400 | From | Neil Horman <> | Subject | Re: [PATCH] RTC: Add mmap method to rtc character driver |
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On Tue, Jul 25, 2006 at 07:57:30PM +0200, Segher Boessenkool wrote: > > At OLS last week, During Dave Jones Userspace Sucks presentation, Jim > >Geddys and some of the Xorg guys noted that they would be able to > >stop using gettimeofday > >so frequently, if they had some other way to get a millisecond > >resolution timer > >in userspace, one that they could perhaps read from a memory mapped > >page. I was > >right behind them and though that seemed like a reasonable > >request, so I've > >taken a stab at it. This patch allows for a page to be mmaped > >from /dev/rtc > >character interface, the first 4 bytes of which provide a regularly > >increasing > >count, once every rtc interrupt. The frequency is of course > >controlled by the > >regular ioctls provided by the rtc driver. I've done some basic > >testing on it, > >and it seems to work well. > > Similar functionality is already available via VDSO on > platforms that support it (currently PowerPC and AMD64?) -- > seems like a better way forward. > In general I agree, but that only works if you operate on a platform that supports virtual syscalls, and has vdso configured. I'm not overly familiar with vdso, but I didn't think vdso could be supported on all platforms/arches. This seems like it might be a nice addition in those cases.
Neil
> > Segher
-- /*************************************************** *Neil Horman *Software Engineer *gpg keyid: 1024D / 0x92A74FA1 - http://pgp.mit.edu ***************************************************/ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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