svn commit: r327950 - in head/sys/powerpc: aim include powerpc ps3

Nathan Whitehorn nwhitehorn at freebsd.org
Sun Jan 14 23:46:41 UTC 2018



On 01/14/18 15:42, Nathan Whitehorn wrote:
>
>
> On 01/14/18 09:57, Nathan Whitehorn wrote:
>>
>>
>> On 01/14/18 09:52, Konstantin Belousov wrote:
>>> On Sun, Jan 14, 2018 at 09:30:53AM -0800, Nathan Whitehorn wrote:
>>>> The immediate consequence of that is that no MI code that knows about
>>>> direct maps can possibly take advantage of the direct map on this
>>>> platform. Do we really want that to save some conditional logic that
>>>> would get optimized out on amd64 and arm64 anyway? I really do not see
>>>> the benefit here.
>>> It is not clear what do you mean.  Are you saying that there is no 
>>> benefit
>>> of providing the conditional logic, or that it is not benefit of 
>>> exclusing
>>> powerpc ?
>>
>> Sorry, that was poorly stated. Let me try again:
>>
>> If we make a PPC_PHYS_TO_DMAP(), but there is an MI PHYS_TO_DMAP() 
>> API, consumer code in the MI parts of the kernel won't be able to 
>> benefit from the PPC direct map, which seems unfortunate. The cost 
>> from a code perspective of having an if (direct_map_available) seems 
>> low, since on systems where direct_map_available is defined to be 1, 
>> the compiler will optimize it to the same code as if gated by #ifdef. 
>> It might be more cumbersome to write the code, however.
>>
>>> I do not object against adding the conditional, but it should not be
>>> too clumsy to use.
>>>
>>
>> OK. Let me try to draft something in the next couple days and see how 
>> much of a pain it is in practice.
>> -Nathan
>>
>
> How about the attached? It makes PHYS_TO_DMAP() return 0 if no mapping 
> exists. This is straightforward, does not introduce extra macros, and 
> can pretty easily replace SFBUF_OPTIONAL_DIRECT_MAP on the assumption 
> that PHYS_TO_DMAP() is cheap. I've modified the other MI-ish consumers 
> in the tree accordingly; compat/linuxkpi/common/src/linux_page.c 
> already does the right thing and needed no modifications.
> -Nathan

Sorry, this is the patch I meant to send.
-Nathan
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