On 2016年07月14日 03:54, Peter Zijlstra wrote:
On Mon, Jun 20, 2016 at 02:20:52PM +0800, Pan Xinhui wrote:
This patch aims to get rid of endianness in queued_write_unlock(). We
want to set __qrwlock->wmode to NULL, however the address is not
&lock->cnts in big endian machine. That causes queued_write_unlock()
write NULL to the wrong field of __qrwlock.
Actually qrwlock can have same layout, IOW we can remove the #if
__little_endian in struct __qrwlock. With such modification, we only
need define some _QW* and _QR* with corresponding values in different
endian systems.
Suggested-by: Will Deacon <will.deacon@xxxxxxx>
Signed-off-by: Pan Xinhui <xinhui.pan@xxxxxxxxxxxxxxxxxx>
Acked-by: Waiman Long <Waiman.Long@xxxxxxx>
---
Urgh, I hate this stuff :/
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);
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
};
I think it is acceptable. and we can do similar things with qrwlock, too.
any thoughts?
/*
- * Writer states & reader shift and bias
+ * 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. :)
thanks
xinhui
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