Laurent Vivier wrote: >> >>> - remove PATCH 3, and add in task_struct a "ktime vtime" where we accumulate >>> guest time (by calling something like guest_enter() and guest_exit() from the >>> virtualization engine), and when in account_system_time() we have cputime > >>> vtime we substrate vtime from cputime and add vtime to user time and guest time. >>> But doing like this we freeze in kernel/sched.c the link between system time, >>> user time and guest time (i.e. system time = system time - vtime, user time = >>> user time + vtime and guest time = guest time + vtime). >>> >> Actually, I think we can set a per-cpu "in_guest" flag for the scheduler >> code, which then knows to add the tick to the guest time. That seems >> the simplest possible solution. >> >> lguest or kvm would set the flag before running the guest (which is done >> with preempt disabled or using preemption hooks), and reset it >> afterwards. >> >> Thoughts? >> > > It was my first attempt (except I didn't have a per-cpu flag, but a per-task > flag), it's not visible but I love simplicity... ;-) > > A KVM VCPU is stopped by preemption, so when we enter in scheduler we have > exited from VCPU and thus this flags is off (so we account 0 to the guest). What > I did then is "set the flag on when we enter in the VCPU, and > "account_system_time()" sets the flag off when it adds this timeslice to cpustat > (and compute correctly guest, user, system time). But I didn't like this idea > because all code executed after we entered in the VCPU is accounted to the guest > until we have an account_system_time() and I suppose we can have real system > time in this part. And I guess a VCPU can be less than 1 ms (unit of cputime) in > a timeslice. > > So ? What's best ? > The normal user/system accounting has the same issue, no? Whereever we happen to land (kernel or user) gets the whole tick. So I think it is okay to have the same limitation for guest time. -- Do not meddle in the internals of kernels, for they are subtle and quick to panic. _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/virtualization
