linux-kernel - Re: [PATCH 1/11] Add generic helpers for arch IPI function calls

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Message-Id: <1209393812.3367.24.camel@localhost.localdomain>
Date:	Mon, 28 Apr 2008 10:43:32 -0400
From:	James Bottomley <James.Bottomley@...senPartnership.com>
To:	David Howells <dhowells@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Jens Axboe <jens.axboe@...cle.com>, linux-arch@...r.kernel.org,
	linux-kernel@...r.kernel.org, npiggin@...e.de,
	torvalds@...ux-foundation.org, peterz@...radead.org,
	sam@...nborg.org, "Paul E. McKenney" <paulmck@...ibm.com>
Subject: Re: [PATCH 1/11] Add generic helpers for arch IPI function calls

On Mon, 2008-04-28 at 15:25 +0100, David Howells wrote:
> We could use a GOT, but I believe that would add an extra memory
> access to any
> memory access or jump - which I'd prefer to avoid.

Not necessarily; this is how we work on PARISC with a GOT as the ELF
spec defines.  The point is that the GOT is linker constructed, so we
only lay down GOT entries when the linker sees that relative
displacements fail, so they don't consume memory (or even get brought
into existence) in the ordinary case.  The flip side of this is that we
do double jump (relative to jump through got) for the long displacements
we can't reach.

James

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