Rusty Russell wrote: > On Tue, 2007-07-10 at 08:53 +0300, Avi Kivity wrote: > >> Rusty Russell wrote: >> >>> No; this is a "I'm doing something magic and need to know before someone >>> else takes the CPU". Almost by definition, you cannot have two of them >>> at the same time. Let someone else try that if and when... >>> >> Why can't you have two of them? Say I'm writing a module to utilize >> branch recording to be able to debug a process in reverse (of course >> that doesn't really need sched hooks; let's pretend it does). Why can't >> I debug a process that uses kvm? >> >> More importantly, now the two subsystems have to know about each other >> so they don't step on each other's toes. >> > > Exactly, if we have two at the same time, they need to know about each > other. Providing infrastructure which lets them avoid thinking about it > is the wrong direction. >
With a kvm-specific hook, they can't stop on each other (there can only be one). With a list, they don't stomp on each other. With a struct preempt_ops but no list, as you propose, they can and will stomp on each other. > >>> But KVM-specific code in the scheduler is just wrong, and I think we all >>> know that. >>> >> Even if I eradicate all mention of kvm from the patch, it's still kvm >> specific. kvm at least is sensitive to the exact point where we switch >> in (it wants interrupts enabled) and it expects certain parameters to >> the callbacks. If $new_abuser needs other conditions or parameters, >> which is quite likely IMO as it will most likely have to do with >> hardware, then we will need to update the hooks anyway. >> > > If it's not general, then this whole approach is wrong: put it in > arch/*/kernel/process.c:__switch_to and finish_arch_switch. I imagine other kvm ports will also need this. It's not arch specific, just kvm specific (but that's not really fair: other archs might want the switch in another place, or they might not need it after all). I guess I can put it in arch specific code, but that means both i386 and x86_64. Once we have another user we can try to generalize it. > The > congruent case which comes to mind is lazy FPU handling. > That one has preempt_ops in hardware: cr0.ts and #NM. > Which brings us to the question: why do you want interrupts enabled? > The sched in hook (vcpu_load) sometimes needs to issue an IPI in order to flush the VT registers from another cpu into memory. -- error compiling committee.c: too many arguments to function ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/ _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
