Date: Mon, 4 Mar 2019 16:30:21 +0200 From: Konstantin Belousov <kostikbel@gmail.com> To: Edward Napierala <trasz@freebsd.org> Cc: src-committers <src-committers@freebsd.org>, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r344758 - in head/sys/fs: nfs nfsserver Message-ID: <20190304143021.GO68879@kib.kiev.ua> In-Reply-To: <CAFLM3-pLSQ8sBawC9YBTgxdMKhtNtoQG1bn2QVDuw-2tDKb4Gg@mail.gmail.com> References: <201903041302.x24D2aG0093620@repo.freebsd.org> <20190304132021.GN68879@kib.kiev.ua> <CAFLM3-pLSQ8sBawC9YBTgxdMKhtNtoQG1bn2QVDuw-2tDKb4Gg@mail.gmail.com>
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On Mon, Mar 04, 2019 at 01:31:37PM +0000, Edward Napierala wrote: > pon., 4 mar 2019 o 13:20 Konstantin Belousov <kostikbel@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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