Re: [PATCH v3] mm/vmalloc: lock contention optimization under multi-threading

[Baoquan He]

On 02/22/24 at 01:52pm, Uladzislau Rezki wrote:
> Hello, Rulinhuang!
> 
> > Hi Uladzislau and Andrew, we have rebased it(Patch v4) on branch 
> > mm-unstable and remeasured it. Could you kindly help confirm if 
> > this is the right base to work on?
> > Compared to the previous result at kernel v6.7 with a 5% performance 
> > gain on intel icelake(160 vcpu), we only had a 0.6% with this commit 
> > base. But we think our modification still has some significance. On 
> > the one hand, this does reduce a critical section. On the other hand, 
> > we have a 4% performance gain on intel sapphire rapids(224 vcpu), 
> > which suggests more performance improvement would likely be achieved 
> > when the core count of processors increases to hundreds or 
> > even thousands.
> > Thank you again for your comments.
> >
> According to the patch that was a correct rebase. Right a small delta
> on your 160 CPUs is because of removing a contention. As for bigger
> systems it is bigger impact, like you point here on your 224 vcpu
> results where you see %4 perf improvement.
> 
> So we should fix it. But the way how it is fixed is not optimal from
> my point of view, because the patch that is in question spreads the
> internals from alloc_vmap_area(), like inserting busy area, across
> many parts now.

I happened to walk into this thread and come up with one draft patch.
Please help check if it's ok.