linux-kernel - [PATCH 0/1] percpu_rw_semaphore: reimplement to not block the readers unnecessarily

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Message-ID: <20121031194135.GA504@redhat.com>
Date:	Wed, 31 Oct 2012 20:41:35 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Mikulas Patocka <mpatocka@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Anton Arapov <anton@...hat.com>, linux-kernel@...r.kernel.org
Subject: [PATCH 0/1] percpu_rw_semaphore: reimplement to not block the
	readers unnecessarily

On 10/30, Oleg Nesterov wrote:
>
> So. down_write/up_right does msleep() and it needs to call
> synchronize_sched() 3 times.
>
> This looks too much. It is not that I am worried about the writers,
> the problem is that the new readers are blocked completely while the
> writer sleeps in msleep/synchronize_sched.
>
> Paul, Mikulas, et al. Could you please look at the new implementation
> below? Completely untested/uncompiled, just for discussion.

I tried to test it, seems to work...

But. I guess the only valid test is: pass the review from Paul/Peter.

Todo:
	- add the lockdep annotations

	- we can speedup the down_write-right-aftet-up_write case

What do you all think?

Oleg.

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