On Mon, Jul 23, 2018 at 03:39:18PM +0800, Xiao Guangrong wrote:
>
>
> On 07/23/2018 12:36 PM, Peter Xu wrote:
> > On Thu, Jul 19, 2018 at 08:15:15PM +0800, guangrong.xiao@xxxxxxxxx wrote:
> > > @@ -1597,6 +1608,24 @@ static void migration_update_rates(RAMState *rs, int64_t end_time)
> > > rs->xbzrle_cache_miss_prev) / iter_count;
> > > rs->xbzrle_cache_miss_prev = xbzrle_counters.cache_miss;
> > > }
> > > +
> > > + if (migrate_use_compression()) {
> > > + uint64_t comp_pages;
> > > +
> > > + compression_counters.busy_rate = (double)(compression_counters.busy -
> > > + rs->compress_thread_busy_prev) / iter_count;
> >
> > Here I'm not sure it's correct...
> >
> > "iter_count" stands for ramstate.iterations. It's increased per
> > ram_find_and_save_block(), so IMHO it might contain multiple guest
>
> ram_find_and_save_block() returns if a page is successfully posted and
> it only posts 1 page out at one time.
ram_find_and_save_block() calls ram_save_host_page(), and we should be
sending multiple guest pages in ram_save_host_page() if the host page
is a huge page?
>
> > pages. However compression_counters.busy should be per guest page.
> >
>
> Actually, it's derived from xbzrle_counters.cache_miss_rate:
> xbzrle_counters.cache_miss_rate = (double)(xbzrle_counters.cache_miss -
> rs->xbzrle_cache_miss_prev) / iter_count;
Then this is suspecious to me too...
>
> > > + rs->compress_thread_busy_prev = compression_counters.busy;
> > > +
> > > + comp_pages = compression_counters.pages - rs->compress_pages_prev;
> > > + if (comp_pages) {
> > > + compression_counters.compression_rate =
> > > + (double)(compression_counters.reduced_size -
> > > + rs->compress_reduced_size_prev) /
> > > + (comp_pages * TARGET_PAGE_SIZE);
> > > + rs->compress_pages_prev = compression_counters.pages;
> > > + rs->compress_reduced_size_prev = compression_counters.reduced_size;
> > > + }
> > > + }
> > > }
> > > static void migration_bitmap_sync(RAMState *rs)
> > > @@ -1872,6 +1901,9 @@ static void flush_compressed_data(RAMState *rs)
> > > qemu_mutex_lock(&comp_param[idx].mutex);
> > > if (!comp_param[idx].quit) {
> > > len = qemu_put_qemu_file(rs->f, comp_param[idx].file);
> > > + /* 8 means a header with RAM_SAVE_FLAG_CONTINUE. */
> > > + compression_counters.reduced_size += TARGET_PAGE_SIZE - len + 8;
> >
> > I would agree with Dave here - why we store the "reduced size" instead
> > of the size of the compressed data (which I think should be len - 8)?
> >
>
> len-8 is the size of data after compressed rather than the data improved
> by compression that is not straightforward for the user to see how much
> the improvement is by applying compression.
>
> Hmm... but it is not a big deal to me... :)
Yeah it might be a personal preference indeed. :)
It's just natural to do that this way for me since AFAIU the
compression ratio is defined as:
compressed data size
compression ratio = ------------------------
original data size
>
> > Meanwhile, would a helper be nicer? Like:
>
> Yup, that's nicer indeed.
Regards,
--
Peter Xu
