Re: [PATCH RFC 01/10] rcu: Make CONFIG_SRCU unconditionally enabled

Kirill Tkhai
2018-08-08T16:30:28Z

On 08.08.2018 19:23, Kirill Tkhai wrote:
> On 08.08.2018 19:13, Josh Triplett wrote:
>> On Wed, Aug 08, 2018 at 01:17:44PM +0300, Kirill Tkhai wrote:
>>> On 08.08.2018 10:20, Michal Hocko wrote:
>>>> On Tue 07-08-18 18:37:36, Kirill Tkhai wrote:
>>>>> This patch kills all CONFIG_SRCU defines and
>>>>> the code under !CONFIG_SRCU.
>>>>
>>>> The last time somebody tried to do this there was a pushback due to
>>>> kernel tinyfication. So this should really give some numbers about the
>>>> code size increase. Also why can't we make this depend on MMU. Is
>>>> anybody else than the reclaim asking for unconditional SRCU usage?
>>>
>>> I don't know one. The size numbers (sparc64) are:
>>>
>>> $ size image.srcu.disabled
>>> text data bss dec hex filename
>>> 5117546 8030506 1968104 15116156 e6a77c image.srcu.disabled
>>> $ size image.srcu.enabled
>>> text data bss dec hex filename
>>> 5126175 8064346 1968104 15158625 e74d61 image.srcu.enabled
>>> The difference is: 15158625-15116156 = 42469 ~41Kb
>>
>> 41k is a *substantial* size increase. However, can you compare
>> tinyconfig with and without this patch? That may have a smaller change.
>
> $ size image.srcu.disabled
> text data bss dec hex filename
> 1105900 195456 63232 1364588 14d26c image.srcu.disabled
>
> $ size image.srcu.enabled
> text data bss dec hex filename
> 1106960 195528 63232 1365720 14d6d8 image.srcu.enabled
>
> 1365720-1364588 = 1132 ~ 1Kb

1Kb is not huge size. It looks as not a big price for writing generic code
for only case (now some places have CONFIG_SRCU and !CONFIG_SRCU variants,
e.g. drivers/base/core.c). What do you think?