Re: [RFC PATCH 0/4] sched+mm: Track lazy active mm existence with hazard pointers

[Mathieu Desnoyers]

On 2024-10-02 17:58, Jens Axboe wrote:
> On 10/2/24 9:53 AM, Mathieu Desnoyers wrote:
> > On 2024-10-02 17:36, Mathieu Desnoyers wrote:
> > > On 2024-10-02 17:33, Matthew Wilcox wrote:
> > > > On Wed, Oct 02, 2024 at 11:26:27AM -0400, Mathieu Desnoyers wrote:
> > > > > On 2024-10-02 16:09, Paul E. McKenney wrote:
> > > > > > On Tue, Oct 01, 2024 at 09:02:01PM -0400, Mathieu Desnoyers wrote:
> > > > > > > Hazard pointers appear to be a good fit for replacing refcount based lazy
> > > > > > > active mm tracking.
> > > > > > >
> > > > > > > Highlight:
> > > > > > >
> > > > > > > will-it-scale context_switch1_threads
> > > > > > >
> > > > > > > nr threads (-t)     speedup
> > > > > > >        24                +3%
> > > > > > >        48               +12%
> > > > > > >        96               +21%
> > > > > > >       192               +28%
> > > > > >
> > > > > > Impressive!!!
> > > > > >
> > > > > > I have to ask...  Any data for smaller numbers of CPUs?
> > > > >
> > > > > Sure, but they are far less exciting ;-)
> > > >
> > > > How many CPUs in the system under test?
> > >
> > > 2 sockets, 96-core per socket:
> > >
> > > CPU(s):                   384
> > >     On-line CPU(s) list:    0-383
> > > Vendor ID:                AuthenticAMD
> > >     Model name:             AMD EPYC 9654 96-Core Processor
> > >       CPU family:           25
> > >       Model:                17
> > >       Thread(s) per core:   2
> > >       Core(s) per socket:   96
> > >       Socket(s):            2
> > >       Stepping:             1
> > >       Frequency boost:      enabled
> > >       CPU(s) scaling MHz:   68%
> > >       CPU max MHz:          3709.0000
> > >       CPU min MHz:          400.0000
> > >       BogoMIPS:             4800.00
> > >
> > > Note that Jens Axboe got even more impressive speedups testing this
> > > on his 512-hw-thread EPYC [1] (390% speedup for 192 threads). I've
> > > noticed I had schedstats and sched debug enabled in my config, so I'll have to re-run my tests.
> >
> > A quick re-run of the 128-thread case with schedstats and sched debug
> > disabled still show around 26% speedup, similar to my prior numbers.
> >
> > I'm not sure why Jens has much better speedups on a similar system.
> >
> > I'm attaching my config in case someone spots anything obvious. Note
> > that my BIOS is configured to show 24 NUMA nodes to the kernel (one
> > NUMA node per core complex).
>
> Here's my .config - note it's from the stock kernel run, which is why it
> still has:
>
> CONFIG_MMU_LAZY_TLB_REFCOUNT=y
>
> set. Have the same numa configuration as you, just end up with 32 nodes
> on this box.

Just to make sure: did you use other command line options when starting
the test program (other than -t N ?).

Thanks,

Mathieu



--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com