From: Steven Rostedt <rostedt@goodmis.org>
To: Jason Baron <jbaron@redhat.com>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>,
"H. Peter Anvin" <hpa@zytor.com>,
"David S. Miller" <davem@davemloft.net>,
David Daney <david.daney@cavium.com>,
Michael Ellerman <michael@ellerman.id.au>,
Jan Glauber <jang@linux.vnet.ibm.com>,
the arch/x86 maintainers <x86@kernel.org>,
Xen Devel <xen-devel@lists.xensource.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>,
peterz@infradead.org, rth@redhat.com
Subject: Re: [PATCH RFC V2 3/5] jump_label: if a key has already been initialized, don't nop it out
Date: Thu, 06 Oct 2011 14:26:52 -0400 [thread overview]
Message-ID: <1317925615.4729.14.camel@gandalf.stny.rr.com> (raw)
In-Reply-To: <20111006181055.GA2505@redhat.com>
On Thu, 2011-10-06 at 14:10 -0400, Jason Baron wrote:
> > Looks like jmp2 is about 5% faster than jmp5 on Sandybridge with this
> > benchmark.
> >
> > But insignificant difference on Nehalem.
> >
> > J
>
> It would be cool if we could make the total width 2-bytes, when
> possible. It might be possible by making the initial 'JUMP_LABEL_INITIAL_NOP'
> as a 'jmp' to the 'l_yes' label. And then patching that with a no-op at boot
> time or link time - letting the compiler pick the width. In that way we could
> get the optimal width...
Why not just do it?
jump_label is encapsulated in arch_static_branch() which on x86 looks
like:
static __always_inline bool arch_static_branch(struct jump_label_key *key)
{
asm goto("1:"
JUMP_LABEL_INITIAL_NOP
".pushsection __jump_table, \"aw\" \n\t"
_ASM_ALIGN "\n\t"
_ASM_PTR "1b, %l[l_yes], %c0 \n\t"
".popsection \n\t"
: : "i" (key) : : l_yes);
return false;
l_yes:
return true;
}
That jmp to l_yes should easily be a two byte jump.
If not I'm sure it would be easy to catch it before modifying the code.
And then complain real loudly about it.
-- Steve
next prev parent reply other threads:[~2011-10-06 18:26 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-10-01 21:55 [PATCH RFC V2 0/5] jump-label: allow early jump_label_enable() Jeremy Fitzhardinge
2011-10-01 21:55 ` [PATCH RFC V2 1/5] jump_label: use proper atomic_t initializer Jeremy Fitzhardinge
2011-10-01 21:55 ` [PATCH RFC V2 2/5] stop_machine: make stop_machine safe and efficient to call early Jeremy Fitzhardinge
2011-10-02 0:36 ` Tejun Heo
2011-10-03 19:24 ` [Xen-devel] " Konrad Rzeszutek Wilk
2011-10-01 21:55 ` [PATCH RFC V2 3/5] jump_label: if a key has already been initialized, don't nop it out Jeremy Fitzhardinge
2011-10-03 15:02 ` Jason Baron
2011-10-03 15:47 ` Steven Rostedt
2011-10-03 16:27 ` Jeremy Fitzhardinge
2011-10-04 14:10 ` Jason Baron
2011-10-04 15:18 ` Jeremy Fitzhardinge
2011-10-04 16:30 ` H. Peter Anvin
2011-10-04 17:53 ` Jason Baron
2011-10-04 18:05 ` Steven Rostedt
2011-10-06 0:16 ` Jeremy Fitzhardinge
2011-10-06 0:17 ` H. Peter Anvin
2011-10-06 0:47 ` Jeremy Fitzhardinge
2011-10-06 17:53 ` Jeremy Fitzhardinge
2011-10-06 18:10 ` Jason Baron
2011-10-06 18:13 ` H. Peter Anvin
2011-10-06 21:39 ` Jeremy Fitzhardinge
2011-10-06 22:08 ` Steven Rostedt
2011-10-06 18:15 ` Jeremy Fitzhardinge
2011-10-06 18:33 ` Jason Baron
2011-10-06 18:35 ` H. Peter Anvin
2011-10-06 18:43 ` Jason Baron
2011-10-06 18:26 ` Steven Rostedt [this message]
2011-10-06 18:29 ` H. Peter Anvin
2011-10-06 18:38 ` Jason Baron
2011-10-06 19:34 ` Steven Rostedt
2011-10-06 20:33 ` Jason Baron
2011-10-06 20:45 ` Steven Rostedt
2011-10-06 18:50 ` Richard Henderson
2011-10-06 19:28 ` Steven Rostedt
2011-10-06 21:42 ` Jeremy Fitzhardinge
2011-10-06 22:06 ` Steven Rostedt
2011-10-06 22:10 ` Jeremy Fitzhardinge
2011-10-06 22:20 ` Steven Rostedt
2011-10-07 17:09 ` [PATCH][RFC] jump_labels/x86: Use either 5 byte or 2 byte jumps Steven Rostedt
2011-10-07 18:52 ` Jason Baron
2011-10-07 19:21 ` Steven Rostedt
2011-10-07 21:48 ` H. Peter Anvin
2011-10-07 22:00 ` Steven Rostedt
2011-10-07 22:03 ` H. Peter Anvin
2011-10-07 19:33 ` Steven Rostedt
2011-10-07 19:40 ` Jeremy Fitzhardinge
2011-10-07 19:58 ` Steven Rostedt
2011-10-07 20:04 ` Peter Zijlstra
2011-10-10 15:36 ` [PATCH RFC V2 3/5] jump_label: if a key has already been initialized, don't nop it out Jason Baron
2011-10-10 19:58 ` Jeremy Fitzhardinge
2011-10-10 20:10 ` Jason Baron
2011-10-01 21:55 ` [PATCH RFC V2 4/5] x86/jump_label: drop arch_jump_label_text_poke_early() Jeremy Fitzhardinge
2011-10-01 21:55 ` [PATCH RFC V2 5/5] sparc/jump_label: " Jeremy Fitzhardinge
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