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

[Mathieu Desnoyers <mathieu.desnoyers@efficios.com>]

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