On Mon, Sep 30, 2024 at 01:14:28AM +0800, yong.hu...@smartx.com wrote: > From: Hyman Huang <yong.hu...@smartx.com> > > Currently, the convergence algorithm determines that the migration > cannot converge according to the following principle: > The dirty pages generated in current iteration exceed a specific > percentage (throttle-trigger-threshold, 50 by default) of the number > of transmissions. Let's refer to this criteria as the "dirty rate". > If this criteria is met more than or equal to twice > (dirty_rate_high_cnt >= 2), the throttle percentage increased. > > In most cases, above implementation is appropriate. However, for a > VM with high memory overload, each iteration is time-consuming. > The VM's computing performance may be throttled at a high percentage > and last for a long time due to the repeated confirmation behavior. > Which may be intolerable for some computationally sensitive software > in the VM. > > As the comment mentioned in the migration_trigger_throttle function, > in order to avoid erroneous detection, the original algorithm confirms > the criteria repeatedly. Put differently, the criteria does not need > to be validated again once the detection is more reliable. > > In the refinement, in order to make the detection more accurate, we > introduce another criteria, called the "dirty ratio" to determine > the migration convergence. The "dirty ratio" is the ratio of > bytes_xfer_period and bytes_dirty_period. When the algorithm > repeatedly detects that the "dirty ratio" of current sync is lower > than the previous, the algorithm determines that the migration cannot > converge. For the "dirty rate" and "dirty ratio", if one of the two > criteria is met, the penalty percentage would be increased. This > makes CPU throttle more responsively and therefor saves the time of > the entire iteration and therefore reduces the time of VM performance > degradation. > > In conclusion, this refinement significantly reduces the processing > time required for the throttle percentage step to its maximum while > the VM is under a high memory load.
I'm a bit lost on why this patch 2-3 is still needed if patch 1 works. Wouldn't that greatly increase the chance of throttle code being inovked already? Why we still need this? Thanks, -- Peter Xu
