Re: [linus:master] [x86] 4817f70c25: stress-ng.mmapaddr.ops_per_sec 63.0% regression

[David Hildenbrand <david@redhat.com>]

On 28.01.25 14:28, Peter Zijlstra wrote:
> On Tue, Jan 28, 2025 at 12:39:51PM +0100, David Hildenbrand wrote:
>> On 28.01.25 12:31, Peter Zijlstra wrote:
> 
>>>> I recall a recent series to select MMU_GATHER_RCU_TABLE_FREE on x86
>>>> unconditionally (@Peter, @Rik).
>>>
>>> Those changes should not have made it to Linus yet.
>>>
>>> /me updates git and checks...
>>>
>>> nope, nothing changed there ... yet
>>
>> Sorry, I wasn't quite clear. CONFIG_PT_RECLAIM made it upstream, which has
>> "select MMU_GATHER_RCU_TABLE_FREE" in kconfig.
>>
>> So I'm wondering if the degradation we see in this report is due to
>> MMU_GATHER_RCU_TABLE_FREE being selected by CONFIG_PT_RECLAIM, and we'd get
>> the same result (degradation) when unconditionally enabling
>> MMU_GATHER_RCU_TABLE_FREE.
> 
> Ah, yes, put a RHEL based config (as is the case here) should already
> have it selected due to PARAVIRT.

Ah, right. Most distros will just have it enabled either way.

But that would then mean that MMU_GATHER_RCU_TABLE_FREE is not the cause 
for the regression here, and something else is going wrong.

-- 
Cheers,

David / dhildenb