Re: [RFC PATCH 0/8] *** A Method for evaluating dirty page rate ***

[Dr. David Alan Gilbert]

* Chuan Zheng (zhengchuan@huawei.com) wrote:
> From: Zheng Chuan <zhengchuan@huawei.com>

Hi,

> Sometimes it is neccessary to evaluate dirty page rate before migration.
> Users could decide whether to proceed migration based on the evaluation
> in case of vm performance loss due to heavy workload.
> Unlikey simulating dirtylog sync which could do harm on runnning vm,
> we provide a sample-hash method to compare hash results for samping page.
> In this way, it would have hardly no impact on vm performance.
> 
> We evaluate the dirtypage rate on running vm.
> The VM specifications for migration are as follows:
> - VM use 4-K page;
> - the number of VCPU is 32;
> - the total memory is 32Gigabit;
> - use 'mempress' tool to pressurize VM(mempress 4096 1024);
> 
> ++++++++++++++++++++++++++++++++++++++++++
> |                      |    dirtyrate    |
> ++++++++++++++++++++++++++++++++++++++++++
> | no mempress          |     4MB/s       |
> ------------------------------------------
> | mempress 4096 1024   |    1204MB/s     |
> ++++++++++++++++++++++++++++++++++++++++++
> | mempress 4096 4096   |    4000Mb/s     |
> ++++++++++++++++++++++++++++++++++++++++++

This is quite neat; I know we've got other people who have asked
for a similar feature!
Have you tried to validate these numbers against a real migration - e.g.
try setting mempress to dirty just under 1GByte/s and see if you can
migrate it over a 10Gbps link?

Dave

> Test dirtyrate by qmp command like this:
> 1.  virsh qemu-monitor-command [vmname] '{"execute":"cal_dirty_rate", 
> "arguments": {"value": [sampletime]}}'
> 2.  virsh qemu-monitor-command [vmname] '{"execute":"get_dirty_rate"}'
> 
> Further test dirtyrate by libvirt api like this:
> virsh getdirtyrate [vmname] [sampletime]
> 
> Zheng Chuan (8):
>   migration/dirtyrate: Add get_dirtyrate_thread() function
>   migration/dirtyrate: Add block_dirty_info to store dirtypage info
>   migration/dirtyrate: Add dirtyrate statistics series functions
>   migration/dirtyrate: Record hash results for each ramblock
>   migration/dirtyrate: Compare hash results for recorded ramblock
>   migration/dirtyrate: Implement get_sample_gap_period() and
>     block_sample_gap_period()
>   migration/dirtyrate: Implement calculate_dirtyrate() function
>   migration/dirtyrate: Implement
>     qmp_cal_dirty_rate()/qmp_get_dirty_rate() function
> 
>  migration/Makefile.objs |   1 +
>  migration/dirtyrate.c   | 424 
> ++++++++++++++++++++++++++++++++++++++++++++++++
>  migration/dirtyrate.h   |  67 ++++++++
>  qapi/migration.json     |  24 +++
>  qapi/pragma.json        |   3 +-
>  5 files changed, 518 insertions(+), 1 deletion(-)
>  create mode 100644 migration/dirtyrate.c
>  create mode 100644 migration/dirtyrate.h
> 
> -- 
> 1.8.3.1
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK