Re: [Xen-devel] [PATCH 6/7] mini-os: Added rmb to xenbus code

["karim.allah.ahmed@xxxxxxxxx" <karim.allah.ahmed@xxxxxxxxx>]

Hi,

Interestingly I find it very difficult to remember any of this code
since It was done during Christmas like 6 months ago :)

In any case, by looking at the patch it seems like rmb was required to
make sure that the reply message is visible to the current processor
when this thread wakes up and starts reading it.

I'll have a look at the other patches and put some comments there as well.

Regards.

On Thu, Jun 5, 2014 at 6:45 PM, Thomas Leonard <talex5@xxxxxxxxx> wrote:
> Hi Karim,
>
> Do you remember what this rmb call is for? It's from your commit here:
>
> https://github.com/KarimAllah/xen/commit/61e8edeb9eabdf575f6f8e7720d977f07d907579#diff-dd67cee31c935093d2c65298a1d5b267R455
>
> https://github.com/KarimAllah/xen/blob/61e8edeb9eabdf575f6f8e7720d977f07d907579/extras/mini-os/xenbus/xenbus.c#L455
>
> Also, if you have any information to add to the other commits, that
> would be very useful:
>
> https://github.com/talex5/xen/commits/sent-Jun-04
>
>
>
> On 5 June 2014 14:55, Julien Grall <julien.grall@xxxxxxxxxx> wrote:
>> Hi Thomas,
>>
>> Thank you for the patch.
>>
>> On 06/04/2014 05:06 PM, Thomas Leonard wrote:
>>> From: Karim Raslan <karim.allah.ahmed@xxxxxxxxx>
>>>
>>> Signed-off-by: Karim Allah Ahmed <karim.allah.ahmed@xxxxxxxxx>
>>> [talex5@xxxxxxxxx: separated from big ARM commit]
>>> Signed-off-by: Thomas Leonard <talex5@xxxxxxxxx>
>>> ---
>>>  extras/mini-os/xenbus/xenbus.c | 1 +
>>>  1 file changed, 1 insertion(+)
>>>
>>> diff --git a/extras/mini-os/xenbus/xenbus.c b/extras/mini-os/xenbus/xenbus.c
>>> index d995020..8a99ee2 100644
>>> --- a/extras/mini-os/xenbus/xenbus.c
>>> +++ b/extras/mini-os/xenbus/xenbus.c
>>> @@ -450,6 +450,7 @@ xenbus_msg_reply(int type,
>>>      remove_waiter(w, req_info[id].waitq);
>>>      wake(current);
>>>
>>> +    rmb();
>>
>> Could you explain in the commit message why this rmb is necessary?
>>
>> Regards,
>>
>> --
>> Julien Grall
>
>
>
> --
> Dr Thomas Leonard        http://0install.net/
> GPG: 9242 9807 C985 3C07 44A6  8B9A AE07 8280 59A5 3CC1
> GPG: DA98 25AE CAD0 8975 7CDA  BD8E 0713 3F96 CA74 D8BA



-- 
Karim Allah Ahmed.

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