Re: [Qemu-devel] [PATCH v4 08/10] migration: fix calculating xbzrle_counters.cache_miss_rate

[Peter Xu <peterx@redhat.com>]

On Tue, Aug 21, 2018 at 04:10:27PM +0800, guangrong.xiao@gmail.com wrote:
> From: Xiao Guangrong <xiaoguangrong@tencent.com>
> 
> As Peter pointed out:
> | - xbzrle_counters.cache_miss is done in save_xbzrle_page(), so it's
> |   per-guest-page granularity
> |
> | - RAMState.iterations is done for each ram_find_and_save_block(), so
> |   it's per-host-page granularity
> |
> | An example is that when we migrate a 2M huge page in the guest, we
> | will only increase the RAMState.iterations by 1 (since
> | ram_find_and_save_block() will be called once), but we might increase
> | xbzrle_counters.cache_miss for 2M/4K=512 times (we'll call
> | save_xbzrle_page() that many times) if all the pages got cache miss.
> | Then IMHO the cache miss rate will be 512/1=51200% (while it should
> | actually be just 100% cache miss).
> 
> And he also suggested as xbzrle_counters.cache_miss_rate is the only
> user of rs->iterations we can adapt it to count target guest page
> numbers
> 
> After that, rename 'iterations' to 'target_page_count' to better reflect
> its meaning
> 
> Suggested-by: Peter Xu <peterx@redhat.com>
> Signed-off-by: Xiao Guangrong <xiaoguangrong@tencent.com>

Reviewed-by: Peter Xu <peterx@redhat.com>

Thanks,

-- 
Peter Xu