| Message ID | 20180807091209.13531-10-xiaoguangrong@tencent.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | migration: compression optimization | expand |
On Tue, Aug 07, 2018 at 05:12:08PM +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 guest page numbers > > After that, rename 'iterations' to 'handle_pages' to better reflect > its meaning > > Suggested-by: Peter Xu <peterx@redhat.com> > Signed-off-by: Xiao Guangrong <xiaoguangrong@tencent.com> > --- > migration/ram.c | 18 +++++++++--------- > 1 file changed, 9 insertions(+), 9 deletions(-) > > diff --git a/migration/ram.c b/migration/ram.c > index 09be01dca2..bd7c18d1f9 100644 > --- a/migration/ram.c > +++ b/migration/ram.c > @@ -300,10 +300,10 @@ struct RAMState { > uint64_t num_dirty_pages_period; > /* xbzrle misses since the beginning of the period */ > uint64_t xbzrle_cache_miss_prev; > - /* number of iterations at the beginning of period */ > - uint64_t iterations_prev; > - /* Iterations since start */ > - uint64_t iterations; > + /* total handled pages at the beginning of period */ > + uint64_t handle_pages_prev; > + /* total handled pages since start */ > + uint64_t handle_pages; The name is not that straightforward to me. I would think about "[guest|host]_page_count" or something better, or we just keep the old naming but with a better comment would be fine too. > /* number of dirty bits in the bitmap */ > uint64_t migration_dirty_pages; > /* last dirty_sync_count we have seen */ > @@ -1587,19 +1587,19 @@ uint64_t ram_pagesize_summary(void) > > static void migration_update_rates(RAMState *rs, int64_t end_time) > { > - uint64_t iter_count = rs->iterations - rs->iterations_prev; > + uint64_t page_count = rs->handle_pages - rs->handle_pages_prev; > > /* calculate period counters */ > ram_counters.dirty_pages_rate = rs->num_dirty_pages_period * 1000 > / (end_time - rs->time_last_bitmap_sync); > > - if (!iter_count) { > + if (!page_count) { > return; > } > > if (migrate_use_xbzrle()) { > xbzrle_counters.cache_miss_rate = (double)(xbzrle_counters.cache_miss - > - rs->xbzrle_cache_miss_prev) / iter_count; > + rs->xbzrle_cache_miss_prev) / page_count; > rs->xbzrle_cache_miss_prev = xbzrle_counters.cache_miss; > } > } > @@ -1657,7 +1657,7 @@ static void migration_bitmap_sync(RAMState *rs) > > migration_update_rates(rs, end_time); > > - rs->iterations_prev = rs->iterations; > + rs->handle_pages_prev = rs->handle_pages; > > /* reset period counters */ > rs->time_last_bitmap_sync = end_time; > @@ -3209,7 +3209,7 @@ static int ram_save_iterate(QEMUFile *f, void *opaque) > break; > } > > - rs->iterations++; > + rs->handle_pages += pages; So it's still counting host pages, is this your intention to only change the name in the patch? > > /* we want to check in the 1st loop, just in case it was the 1st time > and we had to sync the dirty bitmap. > -- > 2.14.4 > Regards,
On 08/08/2018 02:05 PM, Peter Xu wrote: > On Tue, Aug 07, 2018 at 05:12:08PM +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 guest page numbers >> >> After that, rename 'iterations' to 'handle_pages' to better reflect >> its meaning >> >> Suggested-by: Peter Xu <peterx@redhat.com> >> Signed-off-by: Xiao Guangrong <xiaoguangrong@tencent.com> >> --- >> migration/ram.c | 18 +++++++++--------- >> 1 file changed, 9 insertions(+), 9 deletions(-) >> >> diff --git a/migration/ram.c b/migration/ram.c >> index 09be01dca2..bd7c18d1f9 100644 >> --- a/migration/ram.c >> +++ b/migration/ram.c >> @@ -300,10 +300,10 @@ struct RAMState { >> uint64_t num_dirty_pages_period; >> /* xbzrle misses since the beginning of the period */ >> uint64_t xbzrle_cache_miss_prev; >> - /* number of iterations at the beginning of period */ >> - uint64_t iterations_prev; >> - /* Iterations since start */ >> - uint64_t iterations; >> + /* total handled pages at the beginning of period */ >> + uint64_t handle_pages_prev; >> + /* total handled pages since start */ >> + uint64_t handle_pages; > > The name is not that straightforward to me. I would think about > "[guest|host]_page_count" or something better, or we just keep the old > naming but with a better comment would be fine too. The filed actually indicates total pages (target pages more precisely) handled during live migration. 'iterations' confuses us completely. It's target_page_count good to you? > >> /* number of dirty bits in the bitmap */ >> uint64_t migration_dirty_pages; >> /* last dirty_sync_count we have seen */ >> @@ -1587,19 +1587,19 @@ uint64_t ram_pagesize_summary(void) >> >> static void migration_update_rates(RAMState *rs, int64_t end_time) >> { >> - uint64_t iter_count = rs->iterations - rs->iterations_prev; >> + uint64_t page_count = rs->handle_pages - rs->handle_pages_prev; >> >> /* calculate period counters */ >> ram_counters.dirty_pages_rate = rs->num_dirty_pages_period * 1000 >> / (end_time - rs->time_last_bitmap_sync); >> >> - if (!iter_count) { >> + if (!page_count) { >> return; >> } >> >> if (migrate_use_xbzrle()) { >> xbzrle_counters.cache_miss_rate = (double)(xbzrle_counters.cache_miss - >> - rs->xbzrle_cache_miss_prev) / iter_count; >> + rs->xbzrle_cache_miss_prev) / page_count; >> rs->xbzrle_cache_miss_prev = xbzrle_counters.cache_miss; >> } >> } >> @@ -1657,7 +1657,7 @@ static void migration_bitmap_sync(RAMState *rs) >> >> migration_update_rates(rs, end_time); >> >> - rs->iterations_prev = rs->iterations; >> + rs->handle_pages_prev = rs->handle_pages; >> >> /* reset period counters */ >> rs->time_last_bitmap_sync = end_time; >> @@ -3209,7 +3209,7 @@ static int ram_save_iterate(QEMUFile *f, void *opaque) >> break; >> } >> >> - rs->iterations++; >> + rs->handle_pages += pages; > > So it's still counting host pages, is this your intention to only > change the name in the patch? Hmm... the value returned by ram_find_and_save_block() isn't the total target pages posted out? /** * ram_find_and_save_block: finds a dirty page and sends it to f * * Called within an RCU critical section. * * Returns the number of pages written where zero means no dirty pages, * or negative on error ... * * On systems where host-page-size > target-page-size it will send all the * pages in a host page that are dirty. */
On Wed, Aug 08, 2018 at 02:36:51PM +0800, Xiao Guangrong wrote: > > > On 08/08/2018 02:05 PM, Peter Xu wrote: > > On Tue, Aug 07, 2018 at 05:12:08PM +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 guest page numbers > > > > > > After that, rename 'iterations' to 'handle_pages' to better reflect > > > its meaning > > > > > > Suggested-by: Peter Xu <peterx@redhat.com> > > > Signed-off-by: Xiao Guangrong <xiaoguangrong@tencent.com> > > > --- > > > migration/ram.c | 18 +++++++++--------- > > > 1 file changed, 9 insertions(+), 9 deletions(-) > > > > > > diff --git a/migration/ram.c b/migration/ram.c > > > index 09be01dca2..bd7c18d1f9 100644 > > > --- a/migration/ram.c > > > +++ b/migration/ram.c > > > @@ -300,10 +300,10 @@ struct RAMState { > > > uint64_t num_dirty_pages_period; > > > /* xbzrle misses since the beginning of the period */ > > > uint64_t xbzrle_cache_miss_prev; > > > - /* number of iterations at the beginning of period */ > > > - uint64_t iterations_prev; > > > - /* Iterations since start */ > > > - uint64_t iterations; > > > + /* total handled pages at the beginning of period */ > > > + uint64_t handle_pages_prev; > > > + /* total handled pages since start */ > > > + uint64_t handle_pages; > > > > The name is not that straightforward to me. I would think about > > "[guest|host]_page_count" or something better, or we just keep the old > > naming but with a better comment would be fine too. > > The filed actually indicates total pages (target pages more precisely) > handled during live migration. 'iterations' confuses us completely. > > It's target_page_count good to you? Yes. > > > > > > /* number of dirty bits in the bitmap */ > > > uint64_t migration_dirty_pages; > > > /* last dirty_sync_count we have seen */ > > > @@ -1587,19 +1587,19 @@ uint64_t ram_pagesize_summary(void) > > > static void migration_update_rates(RAMState *rs, int64_t end_time) > > > { > > > - uint64_t iter_count = rs->iterations - rs->iterations_prev; > > > + uint64_t page_count = rs->handle_pages - rs->handle_pages_prev; > > > /* calculate period counters */ > > > ram_counters.dirty_pages_rate = rs->num_dirty_pages_period * 1000 > > > / (end_time - rs->time_last_bitmap_sync); > > > - if (!iter_count) { > > > + if (!page_count) { > > > return; > > > } > > > if (migrate_use_xbzrle()) { > > > xbzrle_counters.cache_miss_rate = (double)(xbzrle_counters.cache_miss - > > > - rs->xbzrle_cache_miss_prev) / iter_count; > > > + rs->xbzrle_cache_miss_prev) / page_count; > > > rs->xbzrle_cache_miss_prev = xbzrle_counters.cache_miss; > > > } > > > } > > > @@ -1657,7 +1657,7 @@ static void migration_bitmap_sync(RAMState *rs) > > > migration_update_rates(rs, end_time); > > > - rs->iterations_prev = rs->iterations; > > > + rs->handle_pages_prev = rs->handle_pages; > > > /* reset period counters */ > > > rs->time_last_bitmap_sync = end_time; > > > @@ -3209,7 +3209,7 @@ static int ram_save_iterate(QEMUFile *f, void *opaque) > > > break; > > > } > > > - rs->iterations++; > > > + rs->handle_pages += pages; > > > > So it's still counting host pages, is this your intention to only > > change the name in the patch? > > Hmm... the value returned by ram_find_and_save_block() isn't the total > target pages posted out? Hmm, I overlooked that. Sorry. :) Then it looks fine to me: Reviewed-by: Peter Xu <peterx@redhat.com> > > /** > * ram_find_and_save_block: finds a dirty page and sends it to f > * > * Called within an RCU critical section. > * > * Returns the number of pages written where zero means no dirty pages, > * or negative on error > ... > > * > * On systems where host-page-size > target-page-size it will send all the > * pages in a host page that are dirty. > */ Regards,
diff --git a/migration/ram.c b/migration/ram.c index 09be01dca2..bd7c18d1f9 100644 --- a/migration/ram.c +++ b/migration/ram.c @@ -300,10 +300,10 @@ struct RAMState { uint64_t num_dirty_pages_period; /* xbzrle misses since the beginning of the period */ uint64_t xbzrle_cache_miss_prev; - /* number of iterations at the beginning of period */ - uint64_t iterations_prev; - /* Iterations since start */ - uint64_t iterations; + /* total handled pages at the beginning of period */ + uint64_t handle_pages_prev; + /* total handled pages since start */ + uint64_t handle_pages; /* number of dirty bits in the bitmap */ uint64_t migration_dirty_pages; /* last dirty_sync_count we have seen */ @@ -1587,19 +1587,19 @@ uint64_t ram_pagesize_summary(void) static void migration_update_rates(RAMState *rs, int64_t end_time) { - uint64_t iter_count = rs->iterations - rs->iterations_prev; + uint64_t page_count = rs->handle_pages - rs->handle_pages_prev; /* calculate period counters */ ram_counters.dirty_pages_rate = rs->num_dirty_pages_period * 1000 / (end_time - rs->time_last_bitmap_sync); - if (!iter_count) { + if (!page_count) { return; } if (migrate_use_xbzrle()) { xbzrle_counters.cache_miss_rate = (double)(xbzrle_counters.cache_miss - - rs->xbzrle_cache_miss_prev) / iter_count; + rs->xbzrle_cache_miss_prev) / page_count; rs->xbzrle_cache_miss_prev = xbzrle_counters.cache_miss; } } @@ -1657,7 +1657,7 @@ static void migration_bitmap_sync(RAMState *rs) migration_update_rates(rs, end_time); - rs->iterations_prev = rs->iterations; + rs->handle_pages_prev = rs->handle_pages; /* reset period counters */ rs->time_last_bitmap_sync = end_time; @@ -3209,7 +3209,7 @@ static int ram_save_iterate(QEMUFile *f, void *opaque) break; } - rs->iterations++; + rs->handle_pages += pages; /* we want to check in the 1st loop, just in case it was the 1st time and we had to sync the dirty bitmap.