Isaku Yamahata wrote:
On Thu, Jul 17, 2008 at 07:21:37AM -0700, Jeremy Fitzhardinge wrote:Isaku Yamahata wrote:OK, that means the clockevent and clocksource part would be different. But the runstate accounting should still be the same, no?I had explained about that.I had considered that option. However my conclusion is not share he implementation because xen/ia64 timer interrupt isn'tparavirtualized with VCPUOP_xxx hypercall. But xen/ia64 emulates ar.itm register. (ar.itm is interval time match register which triggers interrupt when interval time counter becomes same value) Since timer interruption is virtualized differently on xen/ia64, the different implementation is a natural consequence.Unfortunately no. At first I had hoped so, but no. Looking consider_steal_time() which implements ia64 steal time accounting, I have no idea to share code cleanly with x86 steal time accounting, do_stolen_accounting().
So, my understanding from looking at your patch that the itc is somewhat like the x86 tsc, in that it's not (necessarily) synchronized between cpus. But unlike the tsc, the itc is always in nanoseconds, but you don't get information from Xen about the current physical cpu's offset from absolute system time. And that means you have the (rather dubious looking) comparisons to test for large jumps in the itc which you try to ignore.
If you had some way to determine the current itc offset, then you could easily have an itc-based clocksource_read(), which would allow you to use the x86 code for stolen time accounting. I don't know how easy that would be to do.
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