Date: Fri, 1 Jun 2012 23:42:34 +0200 From: Giovanni Trematerra <giovanni.trematerra@gmail.com> To: Konstantin Belousov <kostikbel@gmail.com> Cc: Attilio Rao <attilio@freebsd.org>, alc@freebsd.org, Alexander Kabaev <kan@freebsd.org>, freebsd-arch@freebsd.org Subject: Re: [RFC] Kernel shared variables Message-ID: <CACfq092DUHiP42_bW5xSGKPBsiDrQLUPovuxGJfb-9i8e2Gd2A@mail.gmail.com> In-Reply-To: <20120601193522.GA2358@deviant.kiev.zoral.com.ua> References: <CACfq090r1tWhuDkxdSZ24fwafbVKU0yduu1yV2%2BoYo%2BwwT4ipA@mail.gmail.com> <20120601193522.GA2358@deviant.kiev.zoral.com.ua>
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On Fri, Jun 1, 2012 at 9:35 PM, Konstantin Belousov <kostikbel@gmail.com> wrote: > On Fri, Jun 01, 2012 at 07:53:15PM +0200, Giovanni Trematerra wrote: >> Hello, >> I'd like to discuss a way to provide a mechanism to share some read-only >> data between kernel and user space programs avoiding syscall overhead, >> implementing some them, such as gettimeofday(3) and time(3) as ordinary >> user space routine. >> >> The patch at >> http://www.trematerra.net/patches/ksvar_experimental.patch >> > > I very much dislike what you described, it makes ABI maintanence > a nightmare. While I respect your decision to dislike my work, could you please give me some concrete examples of ABI maintenance nightmare? I mean not based on speculation. > Below is some mail I wrote around Spring 2009, making some notes about > desired proposal. I wonder why your proposal isn't on the Ideas Page wiki. By the way, is this proposal valid? http://wiki.freebsd.org/IdeasPage#Avoiding_syscall_overhead_.28GSoC.29 > This is what called vdso in Linux land. I know what vdso is in Linux land but while implementing vdso will give us some additional features in any case it needs a mechanism like the one I implemented (ksvar) to access kernel data while in user space and I think my implementation isn't too much different from what is called VVAR in linux parlance. Please take a look at http://fxr.watson.org/fxr/source/arch/x86/include/asm/vvar.h?v=linux-2.6 http://fxr.watson.org/fxr/source/arch/x86/vdso/vclock_gettime.c?v=linux-2.6;im=10 Could you please review the kernel part of the patch? -- Gianni
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