Re: [PATCH 00/11] Use global pages with PTI

Dave Hansen
2018-03-30T21:40:13Z

On 03/30/2018 01:32 PM, Thomas Gleixner wrote:
> On Fri, 30 Mar 2018, Dave Hansen wrote:
>
>> On 03/30/2018 05:17 AM, Ingo Molnar wrote:
>>> BTW., the expectation on !PCID Intel hardware would be for global pages to help
>>> even more than the 0.6% and 1.7% you measured on PCID hardware: PCID already
>>> _reduces_ the cost of TLB flushes - so if there's not even PCID then global pages
>>> should help even more.
>>>
>>> In theory at least. Would still be nice to measure it.
>>
>> I did the lseek test on a modern, non-PCID system:
>>
>> No Global pages (baseline): 6077741 lseeks/sec
>> 94 Global pages (this set): 8433111 lseeks/sec
>> +2355370 lseeks/sec (+38.8%)
>
> That's all kernel text, right? What's the result for the case where global
> is only set for all user/kernel shared pages?

Yes, that's all kernel text (94 global entries). Here's the number with
just the entry data/text set global (88 global entries on this system):

No Global pages (baseline): 6077741 lseeks/sec
88 Global Pages (kentry ): 7528609 lseeks/sec (+23.9%)
94 Global pages (this set): 8433111 lseeks/sec (+38.8%)