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

[Dr. David Alan Gilbert]

* Zheng Chuan (zhengchuan@huawei.com) wrote:
> 
> 
> On 2020/8/5 0:19, Dr. David Alan Gilbert wrote:
> > * 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
> > 
> Hi, Dave.
> Thank you for your review.
> 
> Note that, the original intention is evaluating dirty rate before migration.

Right, but the reason you want to evaluate the dirty rate is, I guess,
to figure out whether a migration is likely to coverge?

> However, I test dirty rate against a real migration over a bandwidth of 10Gps 
> with various mempress, which shows as below:
> ++++++++++++++++++++++++++++++++++++++++++
> |                      |    dirtyrate    |
> ++++++++++++++++++++++++++++++++++++++++++
> | no mempress          |     8MB/s       |
> ------------------------------------------
> | mempress 4096 1024   |    1188MB/s     |
> ++++++++++++++++++++++++++++++++++++++++++
> 
> It looks still close to actual dirty rate:)

I don't quite understand that comparison you just gave.
But what I was expecting was that a mempress that
just fits teh ~1100MB/s is just the limit of what you can get down
a 10Gbps link.

Dave

> Test results against a real migration will be posted in V2.
> 
> >> 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
> > 
> > 
> > .
> > 
> 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK