| |
|
 |
|
 |
|
|
|
| |
|
|
xen-devel
[Xen-devel] Re: [PATCH] Fix memory order issue inside pv spinlock
Jeremy Fitzhardinge wrote:
On 09/09/09 09:30, Yang, Xiaowei wrote:
Jeremy Fitzhardinge wrote:
On 09/07/09 00:40, Yang, Xiaowei wrote:
barrier() can't prevent reads after it not being reordered with older
writes to different locates before it. Because of it, I can't bring up
4 HVM guests on one SMP machine. Use mb() instead.
Which read is happening too early? Is it "xl->spinners"? How does
it fail?
Yes. If read of xl->spinners happens earlier than write 0 to xl->lock,
notifications to wake up other spinners can be omitted incorrectly,
resulting in others polling indefinitely (because of poll evtchn not
pending) with the lock is uncontended.
OK. And the CPU only guarantees that, without explicit barriers,
write-read ordering is only maintained between accesses to the same
memory location, not separate locations?
Exactly! For more details please refer to Chapter 8.2 of Intel SDM 3A.
Thanks,
Xiaowei
_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel
|
|
|
| |
|
Home