still looking for suggestion.
If totalRefs count the total accesses to blocks, then this update
method (updating at evition) is wrong
LRU::BlkType*
LRU::findVictim(Addr addr, PacketList &writebacks)
{
BlkType *blk = sets[set].blks[assoc-1];
if (blk->isValid()) {
replacements[0]++;
totalRefs += blk->refCount;
...
}
On 1/3/12, Mahmood Naderan <[email protected]> wrote:
> Ok. I think I got it... This example will show that
>
> sets[i]=| head | .... | tail |
>
> init
> (b1,0) (b2,0) (b3,0) (b4,0)
>
> b1 is accessed
> (b1,1) (b2,0) (b3,0) (b4,0)
>
> b3 is accessed
> (b3,1) (b1,1) (b2,0) (b4,0)
>
> b1 is accessed
> (b1,2) (b3,1) (b2,0) (b4,0)
>
> b4 is accessed
> (b4,1) (b1,2) (b3,1) (b2,0)
>
> b2 is accessed
> (b2,1) (b4,1) (b1,2) (b3,1)
>
> Now want to evict? Head shows the MRU and tail shows the LRU. The line
> BlkType *blk = sets[set].blks(assoc-1];
>
> always point to tail. So (b3,1) is found as victim.
>
>
>
> The question now is what do "totalRefs" and "sampledRefs" mean?
> According to stat descriptions, totalRefs means "total number of
> references to valid blocks".
>
> Back to the example, totalRefs=1 because when b3 is selected as
> victim, its refCount is added to totalRefs.
> However totalRefs should be 5. Because valid blocks were referenced 5
> times.
>
> I have no idea about sampledRefs....
>
> Can you clarify that?
>
> On 1/3/12, Nilay Vaish <[email protected]> wrote:
>> On Tue, 3 Jan 2012, Mahmood Naderan wrote:
>>
>>>> refCount is just counting the number of times that block has been
>>>> referenced. The lru policy is maintained without making use of
>>>> refCount.
>>>
>>> i can not understand why....
>>> Doesn't "refCount is just counting the number of times that block has
>>> been referenced" represent a Most Recently Used (or Lease Recently
>>> Used) block?
>>
>> No.
>>
>>>
>>>
>>>> Read the function accessBlock() in lru.cc
>>> From my understandings,
>>>
>>> 1) a block is found based on set and tag
>>> BlkType *blk = sets[set].findBlk(tag);
>>>
>>> 2) If the block is found, it is placed on the MRU position:
>>> sets[set].moveToHead(blk);
>>
>> This line is enforcing the LRU discipline.
>>
>>>
>>> 3) The next 'if" statement is about timing.
>>>
>>> 4) incrementing the refCount which shows this block has been accessed
>>> blk->refCount += 1;
>>>
>>> 5) the block is returned to caller (cache_impl.hh::access())
>>>
>>> So where is replacement?
>>
>> The function accessBlock() does not need to perform any replacement.
>>
>> --
>> Nilay
>>
>
>
> --
> --
> // Naderan *Mahmood;
>
--
--
// Naderan *Mahmood;
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