lkml.org 
[lkml]   [2012]   [Dec]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [RFC PATCH 1/3] x86,smp: move waiting on contended lock out of line
On 12/21/2012 11:40 PM, Michel Lespinasse wrote:
> On Fri, Dec 21, 2012 at 3:50 PM, Rik van Riel <riel@redhat.com> wrote:

>> @@ -53,12 +55,11 @@ static __always_inline void __ticket_spin_lock(arch_spinlock_t *lock)
>>
>> inc = xadd(&lock->tickets, inc);

>> + if (inc.head == inc.tail)
>> + goto out;
>> +
>> + ticket_spin_lock_wait(lock, inc);
>> + out:
>
> why not just:
>
> if (inc.head != inc.tail)
> ticket_spin_lock_wait(lock, inc)

That makes the code nicer, thank you. Applied.

>> +++ b/arch/x86/kernel/smp.c
>> @@ -113,6 +113,20 @@ static atomic_t stopping_cpu = ATOMIC_INIT(-1);
>> static bool smp_no_nmi_ipi = false;
>>
>> /*
>> + * Wait on a congested ticket spinlock.
>> + */
>> +void ticket_spin_lock_wait(arch_spinlock_t *lock, struct __raw_tickets inc)
>> +{
>> + for (;;) {
>> + cpu_relax();
>> + inc.head = ACCESS_ONCE(lock->tickets.head);
>> +
>> + if (inc.head == inc.tail)
>> + break;
>> + }
>
> Why not just:
>
> do {
> cpu_relax()
> inc.head = ...
> } while (inc.head != inc.tail);
>
>
> Other than that, no problems with the principle of it.

In patch #3 I do something else inside the head == tail
conditional block, so this one is best left alone.

Thank you for the comments.



\
 
 \ /
  Last update: 2012-12-22 06:21    [W:1.029 / U:0.640 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site