Re: [Gems-users] state transitions in MOESI

["Datta, Kushal" <kdatta@xxxxxxxx>]

Title: RE: [Gems-users] state transitions in MOESI

Well, since the data is in the O State in P0, most
probably it is updating the data (P0->store).
So, although P1 has the data in S state in its cache,
it does not have the most-recent value. So P1 needs
to get the data from P0.

Thanks and regards,
Kushal.
Graduate Student,
Department of ECE,
UNC Charlotte.



-----Original Message-----
From: gems-users-bounces@xxxxxxxxxxx on behalf of Dave Z.
Sent: Mon 4/9/2007 1:29 PM
To: Gems Users
Subject: Re: [Gems-users] state transitions in MOESI

Hello,

Let me correct my question. If some data is in S state
in the cache, on a store event: GETX event is sent to
the owner directory. The directory then sends the data
to the requesting cache. Why is it necessary to
acquire the data when the cache already has it in S
state?

Thank you,

Dave


--- "Dave Z." <zhu_dave@xxxxxxxxx> wrote:

> Hello,
>
> I have a question regarding the state transitions in
> MOESI-hammer (perhaps the same scenario exists in
> other protocols as well). Let's say we have two
> processors: P0 and P1 that share some data. P0 is
> the owner, so the data is in O state in P0 and in S
> state in P1. If P1 tries to write to the data, GETX
> will be issued. P0 sees the Other_GETX event and
> sends the data back to P1, right? If so, why is
> there a need to send the data even though P1 has the
> data in S state?
>
> Thank you,
>
> Dave
>
>
>
>
> 
>
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