Re: [PATCH] Optimizing x86-64 xenlinux using global pagesfor user mode (take 2)

[Andrew Theurer <habanero@us.ibm.com>]

Nakajima, Jun wrote:
> Andrew Theurer wrote:
>   
>> Ian Pratt wrote:
>>     
>>>> The previous patch had a problem with the builder, which constructs
>>>> the initial page tables with the USER bit on. And Xen couldn't
>>>> distinguish kernel or use pages. It was partially checked avoiding
>>>> the bug, and it's finished with this patch.
>>>>         
>>> Thanks. Have you any updated benchmark numbers as the bug could have
>>> been giving quite a performance boost before.
>>>       
>
> Looks like part of the boost was realized by the bug, but I still see
> consistent and visible improvements with lmbench. If I turn on the
> global bits for the kernel pages as well, I see more improvements, which
> are comparable with or better than before. I think we need to do macro
> benchmarks to see how this helps. 
>
>   
>> FWIW, I had been running more extensive testing on changeset 11225
>> (before global-bit) and 11229 (global-bit with revert/fix for dom0
>> builder), and they do not match the initial testing I did with rev
>> 11118 + global_1 patch.  In fact, I am not seeing really any
>> improvement.  I am not sure what is wrong.  Should I just test
>> xen-unstable-tip+newest_patch and see where we stand?
>>
>>     
>
> Yes, please. You shouldn't have observed any performance difference
> between 11225 and 11229 because the changeset 11226 did not enable the
> global bit. 

OK, then that would explain it :)  I'll run tip+ your latest patch.

-Andrew Theurer