Messages in this thread | | | Date | Thu, 10 Oct 2002 08:45:56 -0700 | From | george anzinger <> | Subject | Re: [PATCH 2/3] High-res-timers part 2 (x86 platform code) take 5.1 |
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"Eric W. Biederman" wrote: > > george anzinger <george@mvista.com> writes: > > > Linus Torvalds wrote: > > > > > > On Wed, 9 Oct 2002, george anzinger wrote: > > > > > > > > This patch, in conjunction with the "core" high-res-timers > > > > patch implements high resolution timers on the i386 > > > > platforms. > > > > > > I really don't get the notion of partial ticks, and quite frankly, this > > > isn't going into my tree until some major distribution kicks me in the > > > head and explains to me why the hell we have partial ticks instead of just > > > making the ticks shorter. > > > > > Well, the notion is to provide timers that have resolution > > down into the micro seconds. Since this take a bit more > > overhead, we just set up an interrupt on an as needed > > basis. This is why we define both a high res and a low res > > clock. Timers on the low res clock will always use the 1/HZ > > tick to drive them and thus do not introduce any additional > > overhead. If this is all that is needed the configure > > option can be left off and only these timers will be > > available. > > > > On the other hand, if a user requires better resolution, > > s/he just turns on the high-res option and incures the > > overhead only when it is used and then only at timer expire > > time. Note that the only way to access a high-res timer is > > via the POSIX clocks and timers API. They are not available > > to select or any other system call. > > > > Making ticks shorter causes extra overhead ALL the time, > > even when it is not needed. Higher resolution is not free > > in any case, but it is much closer to free with this patch > > than by increasing HZ (which, of course, can still be > > done). Overhead wise and resolution wise, for timers, we > > would be better off with a 1/HZ tick and the "on demand" > > high-res interrupts this patch introduces. > > ??? The issue of ticks is separate from the issue of how often > timer interrupts fire. Ticks just becomes the maximum resolution > you can support/express. > > If it makes sense to have two maximum tick resolutions. The normal > application maximum tick rate and the special task maximum tick > rate it is probably worth making this only available as a capability > or an rlimit. > I could support a notion that to use the high-res clock for a timer the user would need a particular capability. After all we do the same for the real time priority.
Does this get us any closer to acceptance in 2.5? -- George Anzinger george@mvista.com High-res-timers: http://sourceforge.net/projects/high-res-timers/ Preemption patch: http://www.kernel.org/pub/linux/kernel/people/rml - 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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