Re: [PATCH v9 2/5] qrwlock x86: Enable x86 to use queue read/writelock

From: Waiman Long
Date: Tue Jan 21 2014 - 11:01:09 EST

On 01/20/2014 11:16 AM, Steven Rostedt wrote:
On Mon, 20 Jan 2014 17:08:06 +0100
Peter Zijlstra<peterz@xxxxxxxxxxxxx> wrote:

On Tue, Jan 14, 2014 at 11:44:04PM -0500, Waiman Long wrote:
This patch makes the necessary changes at the x86 architecture specific
layer to enable the presence of the CONFIG_QUEUE_RWLOCK kernel option
to replace the read/write lock by the queue read/write lock.

It also enables the CONFIG_QUEUE_RWLOCK option by default for x86 which
will force the use of queue read/write lock. That will greatly improve
the fairness of read/write lock and eliminate live-lock situation
where one task may not get the lock for an indefinite period of time.

Signed-off-by: Waiman Long<Waiman.Long@xxxxxx>
Reviewed-by: Paul E. McKenney<paulmck@xxxxxxxxxxxxxxxxxx>
arch/x86/Kconfig | 1 +
arch/x86/include/asm/spinlock.h | 2 ++
arch/x86/include/asm/spinlock_types.h | 4 ++++
3 files changed, 7 insertions(+), 0 deletions(-)
This patch doesn't have nearly enough -, you should rip out all traces
of the old rwlock. There's no point in having it configurable, either
qrwlock is good or not.
Although having something that switches back to the old method gives
more users the way to compare. Especially to catch any regressions.

Make one release with it configurable, then drop it.

-- Steve

Yes, I agree that it will be more prudent to leave the original rwlock implementation there for one or two release cycles before getting rid of them entirely.

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