[Devel] Re: [RFC][PATCH 2/4] res_counter check usage under val

[Paul Menage]

On Tue, Jul 29, 2008 at 7:09 PM, Pavel Emelyanov <xemul at openvz.org> wrote:
>> I get your point. Logically this lock is unnecessary.
>> (And seems this patch itself is buggy..(maybe refresh miss))
>>
>> BTW, I'm sorry if I misunderstand. unsigned long long (on x86-32)
>> can be compared safely ?
>
> Oops... Indeed.
> That discourages me, that we need a spinlock for simple comparisons :(
>

We could add a function to read a res_counter that only takes a
spinlock on architectures where a 64-bit value can't be read
atomically.

Also, for values that are monotonically increasing, I think it should
be possible to read a 64-bit value without locking by checking that
reading the value twice either side of an appropriate memory value
returns the same result both times.

Paul
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