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SubjectRe: [PATCH 5/6] futex: handle timeout inside adaptive lock spin
Thomas Gleixner wrote:
> On Mon, 5 Apr 2010, Darren Hart wrote:
>
>> Signed-off-by: Darren Hart <dvhltc@us.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...

I haven't come across a better alternative since arming the timer before
setting TASK_INTERRUPTIBLE isn't appropriate.

>
>> +/* FIXME: consider creating ktime_less_than(lhs, rhs) */
>
> No need. The .tv64 comparison works in both cases. :)

Ah, for some reason I was thinking that was only the case if
CONFIG_KTIME_SCALAR was set. Very nice, thanks.

--
Darren Hart
IBM Linux Technology Center
Real-Time Linux Team


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