On Thu, Mar 08, 2012 at 10:35:45AM +0900, Takuya Yoshikawa wrote: > Marcelo Tosatti <mtosatti@xxxxxxxxxx> wrote: > > > What is worrying are large memory cases: think of the 50GB slot case. > > 100ms hold time is pretty bad (and reacquiring the lock is relatively > > simple). > > > > OK, I agree basically. > > But let me explain one thing before deciding what I should do next. > > With my method, even when we use a 50GB slot, the hold time will be under > 10ms -- not 100ms -- if the memory actually updated from the last time is > 1GB (256K dirty pages). > > > > 8747274.0 10973.3 33.3 -31% -3% 256K > Note that this unit-test was done on my tiny core-i3 32-bit host. > On servers which can install more than 50GB memory, this will become > much faster: actually my live migration tests done on Xeon saw much > better numbers. Unit-test has been tuned for the worst case. > > I admit that if the dirty memory size is more than 10GB, we may see over > 100ms hold time you are worrying about. > > For that I was proposing introducing a new GET_DIRTY_LOG API which can > restrict the number of dirty pages we get the log - but this is a long > term goal. > > > So, I am OK to try to introduce cond_resched_lock_cb() as you suggested. > But, as I explained above, my current implementation does not introduce > any real regression concerning to mmu_lock hold time: > > Before we could see 10ms hold time in real workloads: > > funcgraph_entry: ! 9783.060 us | kvm_mmu_slot_remove_write_access(); > > I have never seen ms hold time with my method in the same workloads. > > So, it would be helpful if you can apply the patch series and I can work > on top of that: although I cannot use servers with 100GB memory now, > migrating a guest with 16GB memory or so may be possible later: I need > to reserve servers for that. Makes sense. It looks good to me, Avi can you review & ack please? > I also want to know "mmu_lock -- TLB flush"-decoupling plan. We will not > need to introduce cond_resched_lock_cb() in sched.h if that is possible. > > Thanks, > Takuya -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
