linux-kernel - Re: [PATCH v8 10/10] MCS Lock: Make mcs_spinlock.h includable in other files

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Message-ID: <5269AB47.4000007@hp.com>
Date:	Thu, 24 Oct 2013 19:20:39 -0400
From:	Waiman Long <waiman.long@...com>
To:	Tim Chen <tim.c.chen@...ux.intel.com>
CC:	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	Rik van Riel <riel@...hat.com>,
	Peter Hurley <peter@...leysoftware.com>,
	Davidlohr Bueso <davidlohr.bueso@...com>,
	Alex Shi <alex.shi@...aro.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Matthew R Wilcox <matthew.r.wilcox@...el.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Michel Lespinasse <walken@...gle.com>,
	Andi Kleen <andi@...stfloor.org>,
	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	George Spelvin <linux@...izon.com>,
	"H. Peter Anvin" <hpa@...or.com>, Arnd Bergmann <arnd@...db.de>,
	Aswin Chandramouleeswaran <aswin@...com>,
	Scott J Norton <scott.norton@...com>,
	Davidlohr Bueso <davidlohr@...com>,
	Jason Low <jason.low2@...com>
Subject: Re: [PATCH v8 10/10] MCS Lock: Make mcs_spinlock.h includable in
 other files

On 10/24/2013 04:58 PM, Tim Chen wrote:
>
> Do we want to inline the unlock?  Will that prevent proper profile
> accounting of unlock overhead?
>
> Can we keep the mcs_spin_unlock and mcs_spin_lock in the same
> kernel/mcs_spinlock.c file? That makes it easier to read and
> maintain the code.

The unlock code is fast. The lock code, however, can run for a long 
time. It will greatly increase the reported time spent in the calling 
function if it is inlined. The same is true for spinlock. The 
_raw_spin_lock() is a real function while _raw_spin_unlock() is inlined 
in most cases.

Yes, I can bring the lock function back to the mcs_spinlock.h file with 
name like _raw_mcs_spin_lock() and the mcs_spin_lock() in mcs_spinlock.c 
will include the raw function. In that way, the mcs_spin_lock() will 
still be a separate function while both the lock and unlock code will be 
together.

> Can you check if you have applied all the previous MCS patches?
> The last two for barrier corrections and optimizations seem
> to be missing.
>
> MCS Lock: optimizations and extra comments
> https://lkml.org/lkml/2013/10/2/644
> MCS Lock: Barrier corrections
> https://lkml.org/lkml/2013/10/2/650
>
> Thanks.
>
> Tim
>

Apparently, I does have all the MCS patch  in my git tree. I will 
regenerate a new one with the right diff. Thank for the review.

-Longman
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