Re: [Qemu-devel] [PATCH 00/30] Migration thread 20121017 edition

[Chegu Vinod <chegu_vinod@hp.com>]

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On 10/24/2012 6:40 AM, Vinod, Chegu wrote:
>
> Hi
>
> This series apply on top of the refactoring that I sent yesterday.
>
> Changes from the last version include:
>
> - buffered_file.c is gone, its functionality is merged in migration.c
>
>   special attention to the megre of buffered_file_thread() &
>
>   migration_file_put_notify().
>
> - Some more bitmap handling optimizations (thanks to Orit & Paolo for
>
>   suggestions and code and Vinod for testing)
>
> Please review.  Included is the pointer to the full tree.
>
> Thanks, Juan.
>
> The following changes since commit 
> b6348f29d033d5a8a26f633d2ee94362595f32a4:
>
>   target-arm/translate: Fix RRX operands (2012-10-17 19:56:46 +0200)
>
> are available in the git repository at:
>
> http://repo.or.cz/r/qemu/quintela.git migration-thread-20121017
>
> for you to fetch changes up to 486dabc29f56d8f0e692395d4a6cd483b3a77f01:
>
>   ram: optimize migration bitmap walking (2012-10-18 09:20:34 +0200)
>
> v3:
>
> This is work in progress on top of the previous migration series just 
> sent.
>
> - Introduces a thread for migration instead of using a timer and callback
>
> - remove the writting to the fd from the iothread lock
>
> - make the writes synchronous
>
> - Introduce a new pending method that returns how many bytes are 
> pending for
>
>   one save live section
>
> - last patch just shows printfs to see where the time is being spent
>
>   on the migration complete phase.
>
>   (yes it pollutes all uses of stop on the monitor)
>
> So far I have found that we spent a lot of time on bdrv_flush_all() It
>
> can take from 1ms to 600ms (yes, it is not a typo).  That dwarfs the
>
> migration default downtime time (30ms).
>
> Stop all vcpus:
>
> - it works now (after the changes on qemu_cpu_is_vcpu on the previous
>
>   series) caveat is that the time that brdv_flush_all() takes is
>
>   "unpredictable".  Any silver bullets?
>
>   Paolo suggested to call for migration completion phase:
>
>   bdrv_aio_flush_all();
>
>   Sent the dirty pages;
>
>   bdrv_drain_all()
>
>   brdv_flush_all()
>
>   another round through the bitmap in case that completions have
>
>   changed some page
>
>   Paolo, did I get it right?
>
>   Any other suggestion?
>
> - migrate_cancel() is not properly implemented (as in the film that we
>
>   take no locks, ...)
>
> - expected_downtime is not calculated.
>
>   I am about to merge migrate_fd_put_ready & buffered_thread() and
>
>   that would make trivial to calculate.
>
> It outputs something like:
>
> wakeup_request 0
>
> time cpu_disable_ticks 0
>
> time pause_all_vcpus 1
>
> time runstate_set 1
>
> time vmstate_notify 2
>
> time bdrv_drain_all 2
>
> time flush device
>
> /dev/disk/by-path/ip-192.168.10.200:3260-iscsi-iqn.2010-12.org.trasno:iscsi.lvm-lun-1:
>
> 3
>
> time flush device : 3
>
> time flush device : 3
>
> time flush device : 3
>
> time bdrv_flush_all 5
>
> time monitor_protocol_event 5
>
> vm_stop 2 5
>
> synchronize_all_states 1
>
> migrate RAM 37
>
> migrate rest devices 1
>
> complete without error 3a 44
>
> completed 45
>
> end completed stage 45
>
> As you can see, we estimate that we can sent all pending data in 30ms,
>
> it took 37ms to send the RAM (that is what we calculate).  So
>
> estimation is quite good.
>
> What it gives me lots of variation is on the line with device name of 
> "time
>
> flush device".
>
> That is what varies between 1ms to 600ms
>
> This is in a completely idle guest. I am running:
>
>         while (1) {
>
>                 uint64_t delay;
>
>                 if (gettimeofday(&t0, NULL) != 0)
>
> perror("gettimeofday 1");
>
>                 if (usleep(ms2us(10)) != 0)
>
> perror("usleep");
>
>                 if (gettimeofday(&t1, NULL) != 0)
>
> perror("gettimeofday 2");
>
>                 t1.tv_usec -= t0.tv_usec;
>
>                 if (t1.tv_usec < 0) {
>
>                         t1.tv_usec += 1000000;
>
>                         t1.tv_sec--;
>
>                 }
>
>                 t1.tv_sec -= t0.tv_sec;
>
>                 delay = t1.tv_sec * 1000 + t1.tv_usec/1000;
>
>                 if (delay > 100)
>
>                         printf("delay of %ld ms\n", delay);
>
>        }
>
> To see the latency inside the guest (i.e. ask for a 10ms sleep, and 
> see how
>
> long it takes).
>
> [root@d1 ~]# ./timer
>
> delay of 161 ms
>
> delay of 135 ms
>
> delay of 143 ms
>
> delay of 132 ms
>
> delay of 131 ms
>
> delay of 141 ms
>
> delay of 113 ms
>
> delay of 119 ms
>
> delay of 114 ms
>
> But that values are independent of migration.  Without even starting
>
> the migration, idle guest doing nothing, we get it sometimes.
>
> Juan Quintela (27):
>
>   buffered_file: Move from using a timer to use a thread
>
>   migration: make qemu_fopen_ops_buffered() return void
>
>   migration: stop all cpus correctly
>
>   migration: make writes blocking
>
>   migration: remove unfreeze logic
>
>   migration: take finer locking
>
>   buffered_file: Unfold the trick to restart generating migration data
>
>   buffered_file: don't flush on put buffer
>
>   buffered_file: unfold buffered_append in buffered_put_buffer
>
>   savevm: New save live migration method: pending
>
>   migration: include qemu-file.h
>
>   migration-fd: remove duplicate include
>
>   migration: move buffered_file.c code into migration.c
>
>   migration: move migration_fd_put_ready()
>
>   migration: Inline qemu_fopen_ops_buffered into migrate_fd_connect
>
>   migration: move migration notifier
>
>   migration: move begining stage to the migration thread
>
>   migration: move exit condition to migration thread
>
>   migration: unfold rest of migrate_fd_put_ready() into thread
>
>   migration: print times for end phase
>
>   ram: rename last_block to last_seen_block
>
>   ram: Add last_sent_block
>
>   memory: introduce memory_region_test_and_clear_dirty
>
>   ram: Use memory_region_test_and_clear_dirty
>
>   fix memory.c
>
>   migration: Only go to the iterate stage if there is anything to send
>
>   ram: optimize migration bitmap walking
>
> Paolo Bonzini (1):
>
>   split MRU ram list
>
> Umesh Deshpande (2):
>
>   add a version number to ram_list
>
>   protect the ramlist with a separate mutex
>
> Makefile.objs     |   2 +-
>
> arch_init.c       | 133 +++++++++++--------
>
> block-migration.c |  49 ++-----
>
> block.c           |   6 +
>
> buffered_file.c   | 256 -----------------------------------
>
> buffered_file.h   |  22 ---
>
> cpu-all.h         |  13 +-
>
> cpus.c            |  17 +++
>
> exec.c            |  44 +++++-
>
> memory.c          |  17 +++
>
> memory.h          |  18 +++
>
> migration-exec.c  |   4 +-
>
> migration-fd.c    |   9 +-
>
> migration-tcp.c   |  21 +--
>
> migration-unix.c  |   4 +-
>
> migration.c       | 391 
> ++++++++++++++++++++++++++++++++++++++++--------------
>
> migration.h       |   4 +-
>
> qemu-file.h       |   5 -
>
> savevm.c          |  37 +++++-
>
> sysemu.h          |   1 +
>
> vmstate.h         |   1 +
>
> 21 files changed, 522 insertions(+), 532 deletions(-)
>
> delete mode 100644 buffered_file.c
>
> delete mode 100644 buffered_file.h
>
> -- 
>
> 1.7.11.7
>


Tested-by: Chegu Vinod  <chegu_vinod@hp.com>


Using these patches 'have verified live migration (on x86_64 platforms) 
for guest sizes varying from 64G/10vcpus thru 768G/80vcpus and I have 
seen reduction in both the downtime as well as the total migration 
time.  The dirty bitmap optimizations have shown improvements too and 
have helped in the reduction of the downtime (perhaps more can be done 
as a next step..i.e. after the above changes (-minus the printf's) make 
it into upstream).  The new migration stats that were added were useful 
too !

Thanks
Vinod


Vinod


Vinod


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