lkml.org 
[lkml]   [2016]   [Jul]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH v3] locking/qrwlock: Let qrwlock has same layout regardless of the endian
From
Date


在 16/7/14 17:37, Peter Zijlstra 写道:
> On Thu, Jul 14, 2016 at 03:44:42PM +0800, xinhui wrote:
>>> OK, so I poked at this a bit and I ended up with the below; but now
>>> qrwlock and qspinlock are inconsistent; although I suspect qspinlock is
>>> similarly busted wrt endian muck.
>>>
>>> Not sure what to do..
>>>
>> Lets talk about the qspinlock.
>>
>> for x86, We has already assumed that ->locked sit at the low 8 bits, as is
>> smp_store_release((u8 *)lock, 0);
>
> Right, true on x86 though :-) I noticed your PPC patches have a +3 in
> there conditional on __BIG_ENDIAN.
>
>> Then we can do a favor, export ->locked but other fields as reserved.
>> say
>>
>> struct __qspinlock_unlcok_interface {/* what name is better?*/
>> #ifdef __LITTLE_ENDIAN
>> u8 locked;
>> u8 reserved[3]; /* do not touch it, internally use only */
>> #else
>> u8 reserved[3];
>> u8 locked;
>> #endif
>> };
>
> Right, maybe, although something like:
>
> static inline u8 *__qspinlock_lock_byte(struct qspinlock *lock)
> {
> return (u8 *)lock + 3 * IS_BUILTIN(__BIG_ENDIAN);
> }
>
> static inline u8 *__qrwlock_write_byte(struct qrwlock *lock)
> {
> return (u8 *)lock + 3 * IS_BUILTIN(__BIG_ENDIAN);
> }
>
> is shorter?
>

yes, looks simpler. I will take them into my patch. thanks


>
>>> /*
>>> + * Writer states & reader shift and bias.
>>> + *
>>> + * | +0 | +1 | +2 | +3 |
>>> + * ----+----+----+----+----+
>>> + * LE | 12 | 34 | 56 | 78 | 0x12345678
>>> + * ----+----+----+----+----+
>>> + * BE | 78 | 56 | 34 | 12 | 0x12345678
>>> + * ----+----+----+----+----+
>>> + * | wr | rd |
>>> + * +----+----+----+----+
>>> + *
>>> */
>>
>> very clearly. :)
>
> I did one for the qspinlock code too..
>

hmm, pretty nice, I think I can include them into my patch too while I am at it.

thanks
xinhui

> diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c
> index b2caec7315af..9191dc454e96 100644
> --- a/kernel/locking/qspinlock.c
> +++ b/kernel/locking/qspinlock.c
> @@ -120,6 +120,23 @@ static inline __pure struct mcs_spinlock *decode_tail(u32 tail)
> *
> * This internal structure is also used by the set_locked function which
> * is not restricted to _Q_PENDING_BITS == 8.
> + *
> + * | +0 | +1 | +2 | +3 |
> + * ----+----+----+----+----+
> + * LE | 78 | 56 | 34 | 12 | val = 0x12345678
> + * ----+----+----+----+----+
> + * LE | 34 | 12 | locked_pending = 0x1234
> + * ----+----+----+----+----+
> + * | L | P | tail |
> + * +----+----+----+----+
> + *
> + * ----+----+----+----+----+
> + * BE | 12 | 34 | 56 | 78 | val = 0x12345678
> + * ----+----+----+----+----+
> + * BE | 12 | 34 | locked_pending = 0x1234
> + * ----+----+----+----+----+
> + * | tail | P | L |
> + * +----+----+----+----+
> */
> struct __qspinlock {
> union {
>

\
 
 \ /
  Last update: 2016-07-15 09:01    [W:0.066 / U:1.416 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site