From: Andrew Morton <akpm@linux-foundation.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@elte.hu>,
Jason Baron <jbaron@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
Frederic Weisbecker <fweisbec@gmail.com>
Subject: Re: [PATCH 2/5] x86/jump-label: Do not bother updating nops if they are correct
Date: Fri, 27 Jan 2012 12:34:37 -0800 [thread overview]
Message-ID: <20120127123437.481791ba.akpm@linux-foundation.org> (raw)
In-Reply-To: <20120127202031.234193929@goodmis.org>
On Fri, 27 Jan 2012 15:14:44 -0500
Steven Rostedt <rostedt@goodmis.org> wrote:
> --- a/arch/x86/kernel/jump_label.c
> +++ b/arch/x86/kernel/jump_label.c
> @@ -53,7 +53,25 @@ void arch_jump_label_transform(struct jump_entry *entry,
> void arch_jump_label_transform_static(struct jump_entry *entry,
> enum jump_label_type type)
> {
> - __jump_label_transform(entry, type, text_poke_early);
> + static int once;
> + static int update;
> +
> + /*
> + * This function is called at boot up and when modules are
> + * first loaded. Check if the default nop, the one that is
> + * inserted at compile time, is the ideal nop. If it is, then
> + * we do not need to update the nop, and we can leave it as is.
> + * If it is not, then we need to update the nop to the ideal nop.
> + */
> + if (!once) {
> + unsigned char default_nop[] = { JUMP_LABEL_INIT_NOP };
const. It generates less code. With my compiler version, at least.
That was a bit dumb of it, given that memcmp() is declared to take
const args.
> + const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5];
> + once++;
> + if (memcmp(ideal_nop, default_nop, 5) != 0)
> + update = 1;
> + }
> + if (update)
> + __jump_label_transform(entry, type, text_poke_early);
> }
next prev parent reply other threads:[~2012-01-27 20:34 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-27 20:14 [PATCH 0/5] [GIT PULL] x86/jump label: Paranoid checks and 2 or 5 byte nops Steven Rostedt
2012-01-27 20:14 ` [PATCH 1/5] x86/jump-label: Use best default nops for inital jump label calls Steven Rostedt
2012-01-27 20:27 ` H. Peter Anvin
2012-01-27 20:49 ` Steven Rostedt
2012-01-27 20:50 ` H. Peter Anvin
2012-01-27 21:00 ` Steven Rostedt
2012-01-30 21:05 ` Michal Marek
2012-01-27 20:14 ` [PATCH 2/5] x86/jump-label: Do not bother updating nops if they are correct Steven Rostedt
2012-01-27 20:34 ` Andrew Morton [this message]
2012-01-27 20:42 ` Steven Rostedt
2012-01-27 20:14 ` [PATCH 3/5] x86/jump-label: Add safety checks to jump label conversions Steven Rostedt
2012-01-27 20:14 ` [PATCH 4/5] jump labels: Add infrastructure to update jump labels at compile time Steven Rostedt
2012-01-27 20:14 ` [PATCH 5/5] jump labels/x86: Use etiher 5 byte or 2 byte jumps Steven Rostedt
2012-01-27 21:47 ` Steven Rostedt
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