On 04/15/2012 05:32 PM, Avi Kivity wrote: > On 04/13/2012 05:25 PM, Takuya Yoshikawa wrote: >> I forgot to say one important thing -- I might give you wrong impression. >> >> I am perfectly fine with your lock-less work. It is really nice! >> >> The reason I say much about O(1) is that O(1) and rmap based >> GET_DIRTY_LOG have fundamentally different characteristics. >> >> I am thinking really seriously how to make dirty page tracking work >> well with QEMU in the future. >> >> For example, I am thinking about multi-threaded and fine-grained >> GET_DIRTY_LOG. >> >> If we use rmap based GET_DIRTY_LOG, we can restrict write protection to >> only a selected area of one guest memory slot. >> >> So we may be able to make each thread process dirty pages independently >> from other threads by calling GET_DIRTY_LOG for its own area. >> >> But I know that O(1) has its own good point. >> So please wait a bit. I will write up what I am thinking or send patches. >> >> Anyway, I am looking forward to your lock-less work! >> It will improve the current GET_DIRTY_LOG performance. >> >> > > Just to throw another idea into the mix - we can have write-protect-less > dirty logging, too. Instead of write protection, drop the dirty bit, > and check it again when reading the dirty log. It might look like we're > accessing the spte twice here, but it's actually just once - when we > check it to report for GET_DIRTY_LOG call N, we also prepare it for call > N+1. > Walking all gfn's rmap is still expensive, at least, it is not good for the scalability. I want to use a generation number to notify mmu write-protect the PML4s. It is complete out of mmu-lock and comparing lockless write enabling can let it rungs as parallel as possible. -- 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
