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

[Jens Axboe]

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.

-- 
Jens Axboe

Attachment: r7625.config.gz
Description: application/gzip