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 {
--
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