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Re: [Xen-devel] [PATCH 2/2] grant_table: convert grant table rwlock to percpu rwlock
>>> On 18.11.15 at 14:08, <malcolm.crossley@xxxxxxxxxx> wrote:
> On 18/11/15 12:07, Ian Campbell wrote:
>> (Maybe I should have said "like a bit lock with 32 or 64 bits, setting any
>> of which corresponds to acquiring the lock" ;-))
>>
> Not quite, setting the per cpu read area "takes" the read lock for the
> particular
> resource you passed into the percpu rwlock implementation. Writers of another
> resource
> ($resource1) will safely ignore readers of ($resource0).
>
> The global barrier will however make _all_ readers take the per-$resource
> read lock.
> An optimisation could be to have a barrier variable per-$resource (stored in
> the
> struct grant_table in this case).
As said before, I don't view this as an optimization, but as a requirement
(to eliminate the nesting restriction).
Jan
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