From: Rusty Russell <rusty@rustcorp.com.au>
To: Vojtech Pavlik <vojtech@suse.cz>
Cc: linux-kernel@vger.kernel.org
Subject: Re: Percpu data in a vsyscall page
Date: Thu, 03 Nov 2005 12:51:11 +1100 [thread overview]
Message-ID: <1130982671.8734.15.camel@localhost.localdomain> (raw)
In-Reply-To: <20051102105405.GA5320@ucw.cz>
On Wed, 2005-11-02 at 11:54 +0100, Vojtech Pavlik wrote:
> Hi!
>
> I'm working on a RDTSCP support on x86-64, and for that, I'll need
> per-cpu time offset table in a vsyscall page. I saw the percpu.h header,
> and thought - "Hey, I could use that!", but I think I really can't.
>
> The data need to be in a vsyscall page, which is mapped to userspace via
> linker magic, and the percpu stuff uses a different mapping.
Yes. The percpu stuff uses a single add to find the local value of a
variable. This per-cpu offset can be kept in a register (I think
Sparc64 already does this) making it v. fast.
You're going to have to stick with an array I think.
Sorry,
Rusty.
--
A bad analogy is like a leaky screwdriver -- Richard Braakman
prev parent reply other threads:[~2005-11-03 1:51 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-11-02 10:54 Percpu data in a vsyscall page Vojtech Pavlik
2005-11-03 1:51 ` Rusty Russell [this message]
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