linux-kernel - Re: [PATCH 5/6] futex: handle timeout inside adaptive lock spin

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Date:	Tue, 6 Apr 2010 10:27:58 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Darren Hart <dvhltc@...ibm.com>
cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Eric Dumazet <eric.dumazet@...il.com>,
	"Peter W. Morreale" <pmorreale@...ell.com>,
	Rik van Riel <riel@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Gregory Haskins <ghaskins@...ell.com>,
	Sven-Thorsten Dietrich <sdietrich@...ell.com>,
	Chris Mason <chris.mason@...cle.com>,
	John Cooper <john.cooper@...rd-harmonic.com>,
	Chris Wright <chrisw@...s-sol.org>, Avi Kivity <avi@...hat.com>
Subject: Re: [PATCH 5/6] futex: handle timeout inside adaptive lock spin

On Mon, 5 Apr 2010, Darren Hart wrote:

> Signed-off-by: Darren Hart <dvhltc@...ibm.com>
> ---
>  kernel/futex.c |   24 +++++++++++++++++++++---
>  1 files changed, 21 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/futex.c b/kernel/futex.c
> index c33ac2a..af61dcd 100644
> --- a/kernel/futex.c
> +++ b/kernel/futex.c
> @@ -2385,6 +2385,7 @@ out:
>  /**
>   * trylock_futex_adaptive() - Try to acquire the futex lock in a busy loop
>   * @uaddr: the futex user address
> + * @timeout: absolute timeout or NULL if none
>   *
>   * Try to acquire a futex lock in a loop until the owner changes or the owner
>   * is descheduled. To lock the futex, set the value to the current TID.
> @@ -2394,10 +2395,11 @@ out:
>   *  1 - Futex lock acquired
>   * <0 - On error
>   */
> -static int trylock_futex_adaptive(u32 __user *uaddr)
> +static int trylock_futex_adaptive(u32 __user *uaddr, ktime_t *timeout)
>  {
>  	int ret = 0;
>  	u32 curval;
> +	ktime_t now;
>  
>  	for (;;) {
>  		struct thread_info *owner;
> @@ -2433,6 +2435,22 @@ static int trylock_futex_adaptive(u32 __user *uaddr)
>  		if (need_resched())
>  			break;
>  
> +		if (timeout) {
> +			now = ktime_get();

  Hmm. Calling that in every iteration might hurt especially on non
  TSC systems, but well...

> +/* FIXME: consider creating ktime_less_than(lhs, rhs) */

  No need. The .tv64 comparison works in both cases. :)

Thanks,

	tglx
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