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From: Jeremy Fitzhardinge <jeremy@goop.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: "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>,
	Jason Baron <jbaron@redhat.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>
Subject: Re: [PATCH RFC 0/8] jump-label: allow early jump_label_enable()
Date: Thu, 29 Sep 2011 21:40:57 -0700	[thread overview]
Message-ID: <4E854859.4020105@goop.org> (raw)
In-Reply-To: <1317343975.4588.36.camel@gandalf.stny.rr.com>

On 09/29/2011 05:52 PM, Steven Rostedt wrote:
> On Thu, 2011-09-29 at 16:26 -0700, Jeremy Fitzhardinge wrote:
>> From: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
>>
>> One big question which arises is whether the _early() function is
>> necessary at all.  All the stop_machine/mutex/etc stuff that
>> arch_jump_label_transform() ends up doing is redundant pre-SMP, but it
>> shouldn't hurt.  Maybe we can just drop the _early function?  It works
>> on x86, at least, because jump_label_enable() works, which uses the full
>> form.  And dropping it would reduce this to a very much smaller series.
> It does slow down the boot process, which is not a good thing when
> everyone is pushing for the fastest restarts.

Would it really though?  stop_machine() doesn't do very much when there
are no other cpus.

Not that I measured or anything, but there was no obvious big lag at boot.

> What we should probably do is have a global read_mostly variable called,
> smp_activated or something, then things that can be called before and
> after can read this variable to determine if it can skip certain
> protections.

Could do that if it turns out to be a problem.

> While we're at it, perhaps we could add a memory_initialized for things
> like tracers that want to trace early but need to wait till it can
> allocate buffers. If we had this flag, it could instead do an early
> memory init to create the buffers.

That seems orthogonal to the jump_label changes.

    J

WARNING: multiple messages have this Message-ID (diff)
From: Jeremy Fitzhardinge <jeremy@goop.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Xen Devel <xen-devel@lists.xensource.com>,
	Jan Glauber <jang@linux.vnet.ibm.com>,
	Jason Baron <jbaron@redhat.com>,
	the arch/x86 maintainers <x86@kernel.org>,
	David Daney <david.daney@cavium.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Michael Ellerman <michael@ellerman.id.au>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>,
	"David S. Miller" <davem@davemloft.net>
Subject: Re: [PATCH RFC 0/8] jump-label: allow early jump_label_enable()
Date: Thu, 29 Sep 2011 21:40:57 -0700	[thread overview]
Message-ID: <4E854859.4020105@goop.org> (raw)
In-Reply-To: <1317343975.4588.36.camel@gandalf.stny.rr.com>

On 09/29/2011 05:52 PM, Steven Rostedt wrote:
> On Thu, 2011-09-29 at 16:26 -0700, Jeremy Fitzhardinge wrote:
>> From: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
>>
>> One big question which arises is whether the _early() function is
>> necessary at all.  All the stop_machine/mutex/etc stuff that
>> arch_jump_label_transform() ends up doing is redundant pre-SMP, but it
>> shouldn't hurt.  Maybe we can just drop the _early function?  It works
>> on x86, at least, because jump_label_enable() works, which uses the full
>> form.  And dropping it would reduce this to a very much smaller series.
> It does slow down the boot process, which is not a good thing when
> everyone is pushing for the fastest restarts.

Would it really though?  stop_machine() doesn't do very much when there
are no other cpus.

Not that I measured or anything, but there was no obvious big lag at boot.

> What we should probably do is have a global read_mostly variable called,
> smp_activated or something, then things that can be called before and
> after can read this variable to determine if it can skip certain
> protections.

Could do that if it turns out to be a problem.

> While we're at it, perhaps we could add a memory_initialized for things
> like tracers that want to trace early but need to wait till it can
> allocate buffers. If we had this flag, it could instead do an early
> memory init to create the buffers.

That seems orthogonal to the jump_label changes.

    J

  reply	other threads:[~2011-09-30  4:41 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-09-29 23:26 [PATCH RFC 0/8] jump-label: allow early jump_label_enable() Jeremy Fitzhardinge
2011-09-29 23:26 ` [PATCH RFC 1/8] jump_label: use proper atomic_t initializer Jeremy Fitzhardinge
2011-09-29 23:26 ` [PATCH RFC 2/8] jump_label: if a key has already been initialized, don't nop it out Jeremy Fitzhardinge
2011-09-29 23:26 ` [PATCH RFC 3/8] x86/jump_label: add arch_jump_label_transform_early() Jeremy Fitzhardinge
2011-09-29 23:26 ` [PATCH RFC 4/8] sparc/jump_label: " Jeremy Fitzhardinge
2011-09-29 23:31   ` David Miller
2011-09-29 23:26 ` [PATCH RFC 5/8] mips/jump_label: " Jeremy Fitzhardinge
2011-09-29 23:26 ` [PATCH RFC 6/8] powerpc/jump_label: " Jeremy Fitzhardinge
2011-09-29 23:26 ` [PATCH RFC 7/8] s390/jump-label: " Jeremy Fitzhardinge
2011-09-30 14:48   ` Jan Glauber
2011-09-30 16:03     ` Jeremy Fitzhardinge
2011-09-30 16:03       ` Jeremy Fitzhardinge
2011-10-01 11:22       ` Jan Glauber
2011-09-29 23:26 ` [PATCH RFC 8/8] jump_label: drop default arch_jump_label_transform_early Jeremy Fitzhardinge
2011-09-30  0:52 ` [PATCH RFC 0/8] jump-label: allow early jump_label_enable() Steven Rostedt
2011-09-30  4:40   ` Jeremy Fitzhardinge [this message]
2011-09-30  4:40     ` Jeremy Fitzhardinge
2011-09-30 15:28     ` Steven Rostedt
2011-09-30 16:09       ` Jeremy Fitzhardinge

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