Hi,
As gem5 uses non-inclusive hierarchy, the 1st point is not applicable.
Your second point makes sense. It is not mandatory to invalidate at the
LLC. The block at the LLC should be invalidated if the hierarchy is an
exclusive one.
What gem5 does is at a given instant of time, It makes sure that only one
cache is the owner (across all L1s and L2)
So it invalidates at the L2 also.
On Sun, Jan 4, 2015 at 8:53 PM, Nizamudheen Ahmed via gem5-users <
[email protected]> wrote:
> Hi Andreas,
>
> iMHO, There are a couple of cases where it may not be required to
> invalidate line in lower levels
>
> 1. Inclusive caches: I would assume that the lower level inclusive caches
> should , by definition of inclusiveness, hold all the lines a higher level
> cache has.
>
> 2. Shared last level cache: the last level cache (the cache just ahead of
> main memory) may choose to not invalidate the line on a upgradereq.
> Rational: as long as exclusivity is maintained by private cache in earlier
> level, share LLC is strictly not required to invalidate the line on
> upgradereq.
>
> Kindly correct me if implicit assumptions I am making is distorting the
> reasoning:)
>
> Thanks and regards
> Nizam
>
>
> Sent from my iPad
>
> On 04-Jan-2015, at 6:15 pm, Andreas Hansson <[email protected]>
> wrote:
>
> Hi Nizam,
>
> What do you suggest the lower-level cache should do? The UpgradeReq is
> ultimately there to ensure that a cache can get a line in exclusive state
> (E) to perform a write (M).
>
> Andreas
>
> From: Nizamudheen Ahmed via gem5-users <[email protected]>
> Reply-To: Nizamudheen Ahmed <[email protected]>, gem5 users mailing
> list <[email protected]>
> Date: Sunday, 4 January 2015 08:47
> To: gem5 users mailing list <[email protected]>
> Subject: [gem5-users] UpgradeReq command and impact on next-level cache
>
> Hi,
>
> I am using classic memory-model in GEM5. I observed that an UpgradeReq
> command invalidates the line in cache. This behavior is acceptable for
> peer-caches in the same-level. However, i am not sure if the UpgradeReq
> should invalidate the cache line in the lower level caches (Caches closer
> to the main-memory are lower levels, in my terminology). Can someone
> through light on this?
>
> BR/Nizam
>
>
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