On Mon, Mar 04, 2019 at 01:31:37PM +0000, Edward Napierala wrote:
> pon., 4 mar 2019 o 13:20 Konstantin Belousov <kostik...@gmail.com> napisał(a):
> > > + p = curthread;
> > Why do you name it 'p', which is typical for process, and not 'td', you are
> > changing most of the code anyway.
>
> To keep the diff size smaller. You're right, this touches a lot of stuff,
> but most of those added lines are temporary anyway - they will be
> removed later, when the td is pushed down even more.
But if you create code churn, doing it only half way is worse.
>
> > Also I am curious why. It is certainly fine to remove td when it is used
> > as a formal placeholder argument only. But when the first action in the
> > function is evaluation of curthread() it becomes less obvious.
>
> Again, many/most of those are temporary. I'm trying to push td down
> in small steps, "layer by layer", so it's easy to review.
>
> > curthread() become very cheap on modern amd64, I am not so sure about
> > older machines or non-x86 cases.
>
> The main reason is readability. Right now there's no easy way to tell whether
> a function can be passed any td, or if it must be curthread.
I must admit that this is the weirdnest argument against 'td' that I ever
heard. I saw more or less reasonable argumentation
- that using less arguments make one more register for argument passing
(amd64 has 6 input arg regs),
- that less arguments make smaller call code.
But trust me, in all cases where function can take td != curthread, it is
either obvious or well-known for anybody who works with that code.
Before you start doing a lot of small changes (AKA continous churn)
please formulate your goals and get some public feedback. My immediate
question that I want answered before you ever start touching the code,
is what you plan to do with
sys_syscall(struct thread *td, uap)
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