Rene Herman wrote on 20.08.2008 22:52:
quoted text
> On 20-08-08 20:21, Stanichenko Marat wrote:
> 
>>>> -        credit_entropy_bits(&input_pool,
>>>> -                    min_t(int, fls(delta>>1), 11));
>>>> +        nbits = min_t(int, fls(delta>>1), 11);
>>>> +        spin_lock_irqsave(&state->lock, flags);
>>>> +        state->nbits += nbits;
>>>> +        spin_unlock_irqrestore(&state->lock, flags);
>>>> +        credit_entropy_bits(&input_pool,nbits);
>>>
>>>
>>> Couldn't state->nbits be an atomic_t? The locking looks like it might 
>>> be a little expensive. Maybe they should be per-cpu? I have no idea 
>>> about the frequencies here...
>>>
>> I've thought about this:
>> about atomic_t:
>> - atomic_t might be 2^24 as a maximum value (on SPARC arch). I've 
>> created VMWare test machine and left it without any special load for a 
>> day. Then I measured the value of produced entropy. The max number was 
>> about 30000. 2^24/30000 ~ 559 days without overflowing. I don't know 
>> if it suits for our purpose... that's why I rejected this approach.
> 
> Okay, no real opinion there but there's also an atomic_long_t.
> 
Thanks again. I'll try to learn abouth atomic_long_t and if it's really 
works as I think I'll use them instead of disable irq and locking 
because it really seems ugly. :)
quoted text
>> about per-cpu variables:
>> - the function called with interrupts enable so if I use spinlock I 
>> must disable interrupts, am I right?
> 
> The question does not seem related to per-cpu variables. Note that per 
> cpu data can be accessed locklessly.
>
It was misprinting I've ment the following: the function might be called 
with interrupts enable so if I use PER_CPU variables I have do disable 
interrups on this CPU.
quoted text
> I don't know if there's a good tutorial on them but see <linux/percpu.h> 
> You declare them with DEFINE_PER_CPU() and access them with 
> {get,put}_cpu_var().
> 
> In fact, now that I'm grepping, Documentation/local_ops.txt looks 
> interesting here.
> 
> Rene.
I am really grateful to you for the help. I'll try to improve my patch 
and resend it.

Stanichenko Marat


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