lkml.org 
[lkml]   [2014]   [Apr]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v9 04/19] qspinlock: Extract out the exchange of tail code word
On 04/17/2014 11:49 AM, Peter Zijlstra wrote:
> On Thu, Apr 17, 2014 at 11:03:56AM -0400, Waiman Long wrote:
>> @@ -192,36 +220,25 @@ void queue_spin_lock_slowpath(struct qspinlock *lock, u32 val)
>> node->next = NULL;
>>
>> /*
>> + * We touched a (possibly) cold cacheline; attempt the trylock once
>> + * more in the hope someone let go while we weren't watching as long
>> + * as no one was queuing.
>> */
>> + if (!(val& _Q_TAIL_MASK)&& queue_spin_trylock(lock))
>> + goto release;
> But you just did a potentially very expensive op; @val isn't
> representative anymore!

That is not true. I pass in a pointer to val to trylock_pending() (the
pointer thing) so that it will store the latest value that it reads from
the lock back into val. I did miss one in the PV qspinlock exit loop. I
will add it back when I do the next version.

-Longman


\
 
 \ /
  Last update: 2014-04-18 00:01    [W:0.288 / U:0.776 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site