[Ksummit-discuss] No more module removal -- Unconference track

[Masami Hiramatsu]

(2014/08/25 20:05), Jiri Kosina wrote:
> On Mon, 25 Aug 2014, Masami Hiramatsu wrote:
> 
>> What I found is that the module unloading involving 2 stop_machine()s 
>> for each module removing. It must not be needed. However, since the 
>> module's ref-counter is over-optimized for BIG SMP machine, we can't 
>> remove it without replacing it. But it means some performance regression 
>> can happen on such big-scale SMP machines (not the laptop nor normal smp 
>> machine).
> 
> Is that really a big problem in practice?
> 
> I.e. are there valid usecase scenarios where module load / unload should 
> be considered a hotpath where every ms of performance would matter?

There could be. However, in usual usecases, I guess people will not want
to unload it. Systemtap or something "additional" module users will
need to unload modules. (kpatch could be one of them, but I also think
no one want to remove applied patches anyway.)

I just tried to show that the kmodule unload is the one who uses
stop_machine heavily but it is not necessary :)

Thank you,

-- 
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Research Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt at hitachi.com