Re: [Xen-devel] new netfront and occasional receive path lockup

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

 On 09/10/2010 12:37 PM, Xu, Dongxiao wrote:
>> However, I am concerned about these manipulations of a cross-cpu
>> shared variable without any barriers or other ordering constraints. 
>> Are you sure this code is correct under any reordering (either by the
>> compiler or CPUs); and if the compiler decides to access it more or
>> less often than the source says it should?    
> Do you mean the flag "np->rx.sring->private.netif.smartpoll_active"?
> It is a flag in shared ring structure, Therefore operations towards
> this flag are the same as other component in shared ring, such as
> under spinlock, etc.

Spinlocks are no use for inter-domain synchronization, only within a
domain.  The other ring operations are carefully ordered with
appropriate memory barriers in specific places; that's why I'm a bit
concerned about their absence for the smartpoll_active flag.  Even if
they are not necessary, I'd like to see an analysis as to why.

    J

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