Re: [RFC PATCH 4/5] RCU: Add TASK_RCU_OFFSET
From: Lai Jiangshan
Date: Thu Apr 07 2011 - 21:24:15 EST
On 04/08/2011 12:26 AM, Paul E. McKenney wrote:
> On Thu, Apr 07, 2011 at 08:47:37AM -0700, Paul E. McKenney wrote:
>> On Thu, Apr 07, 2011 at 01:49:51PM +0800, Lai Jiangshan wrote:
>>> On 04/07/2011 08:30 AM, Paul E. McKenney wrote:
>>>> On Wed, Apr 06, 2011 at 02:27:39PM -0700, H. Peter Anvin wrote:
>>>>> On 04/06/2011 02:06 PM, Peter Zijlstra wrote:
>>>>>> On Wed, 2011-04-06 at 13:13 -0700, Paul E. McKenney wrote:
>>>>>>> And the following patch builds correctly for defconfig x86 builds,
>>>>>>> while allowing rcupdate.h to see the sched.h definitions as needed
>>>>>>> to inline rcu_read_lock() and rcu_read_unlock().
>>>>>> Looks like an entirely reasonable patch to me ;-)
>>>>> Quite... a lot better than the original proposal!
>>>> Glad you both like it!
>>>> When I do an allyesconfig build, I do get errors during the "CHECK"
>>>> phase, when it is putting things into the usr/include in the build tree.
>>>> I believe that this is because I am exposing different header files to
>>>> the library-export scripts. The following patch silences some of them,
>>>> but I am really out of my depth here.
>>>> Sam, Jan, Michal, help?
>>>> Thanx, Paul
>>> Easy to split rcupdate.h, hard to resolve the dependence problem.
>>> You can apply the next additional patch when you test:
>> I am sure that you are quite correct. ;-)
>> I am moving _rcu_read_lock() and _rcu_read_unlock() into
>> include/linux/rcutree.h and include/linux/rcutiny.h, and I am sure that
>> more pain will ensue.
>> One thing I don't understand... How does is it helping to group the
>> task_struct RCU-related fields into a structure? Is that generating
>> better code on your platform due to smaller offsets or something?
You don't like task_rcu_struct patch? I think it can make code clearer,
and it can also check the code even when CONFIG_PREEMPT_RCU=n.
For rcu_read_[un]lock(), it generates the same code, no better, no worse.
It is just a cleanup patch, it is helpless for making rcu_read_[un]lock() inline,
if you don't like it, I will give up it.
>> Also, does your patchset address the CHECK warnings?
> I take it back... I applied the following patch on top of my earlier
> one, and a defconfig x86 build completed without error. (Though I have
> not tested the results of the build.)
> One possible difference -- I did this work on top of a recent Linus
> git commit (b2a8b4b81966) rather than on top of my -rcu tree. Also,
> I have not yet tried an allyesconfig build, which will no doubt locate
> some more problems.
> Thanx, Paul
when defconfig or allyesconfig, CONFIG_PREEMPT=n and CONFIG_TREE_PREEMPT_RCU=n
when you make them "y":
In file included from include/linux/rcupdate.h:764:0,
include/linux/rcutree.h:50:20: error: static declaration of â__rcu_read_lockâ follows non-static declaration
include/linux/rcupdate.h:76:13: note: previous declaration of â__rcu_read_lockâ was here
include/linux/rcutree.h:63:20: error: static declaration of â__rcu_read_unlockâ follows non-static declaration
include/linux/rcupdate.h:77:13: note: previous declaration of â__rcu_read_unlockâ was here
make: *** [arch/x86/kernel/asm-offsets.s] Error 1
make: *** [prepare0] Error 2
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