Hi, I am working on the x86 page walker in gem5. I understand that the page walker accesses the page walker cache (PWC) first and, in case of a miss, it accesses the memory hierarchy (L1, then L2, then L3 caches and lastly the memory). This happens through the packetpointer *read*, which reads the physical address of the entry at each level (PML4, PDP.. etc.). Now, what I would like to inquire about is how to identify where this read request for the PTE hits in the memory hierarchy. In other words, for each step, I would like to know whether this entry was a hit in L1, L2, or L3. So, is there any field or function/method in the packet that holds this information? If not, how can I get this information? Thanks, -- *Best,Abdelrahman Hussein*

bool isYourType() const {return _flags.isSet(your_flag);}

setupWalk(Addr vaddr){

    Request::Flags flags = Request::PHYSICAL;
    flags.set(Request::your_flag);
    ...
}

book checkYourType() const { return m_pkt->req->isYourType();}

in_port(mandatoryQueue_in, RubyRequest ...)
    if (mandatorQueue_in.isReady(clockEdge()))
        peek(mandatoryQueue_in ...)

            if(is_valid(L1Dcache_entry))
                if(in_msg.checkYourType() == true)
                    # you have it in your local private cache
                else
                    # forward the request to L2

in_port(L1RequestL2Network_in, ...)
    if(L1RequestL2Network_in.isReady(clockEdge()))
        peek(L1RequestL2Network_in ...)
            if(is_valid(cache_entry))
                if(in_msg.checkYourType() == true)
                    # you have it in your shared L2
                else
                    # forward to where it should be

Hi Abdelrahman, I have done something similar with ruby enabled. Hope this helps. Basically you need to set your own message flags in the pagetable walker and checks that flag in the SLICC code when a cacheline hits. Below is an example of how to do it in the L1 and L2. in request.hh ``` bool isYourType() const {return _flags.isSet(your_flag);} ``` in pagetable_walker.cc ``` setupWalk(Addr vaddr){ Request::Flags flags = Request::PHYSICAL; flags.set(Request::your_flag); ... } ``` in RubyRequest.hh ``` book checkYourType() const { return m_pkt->req->isYourType();} ``` in PROTOCOL-L1Cache.sm ``` in_port(mandatoryQueue_in, RubyRequest ...) if (mandatorQueue_in.isReady(clockEdge())) peek(mandatoryQueue_in ...) if(is_valid(L1Dcache_entry)) if(in_msg.checkYourType() == true) # you have it in your local private cache else # forward the request to L2 ``` in PROTOCOL-L2Cache.sm ``` in_port(L1RequestL2Network_in, ...) if(L1RequestL2Network_in.isReady(clockEdge())) peek(L1RequestL2Network_in ...) if(is_valid(cache_entry)) if(in_msg.checkYourType() == true) # you have it in your shared L2 else # forward to where it should be ``` Abdelrahman S. Hussein via gem5-users @ 2024-10-02 03:12 : > Hi, > > I am working on the x86 page walker in gem5. I understand that the page walker accesses the page walker cache (PWC) first > and, in case of a miss, it accesses the memory hierarchy (L1, then L2, then L3 caches and lastly the memory). This > happens through the packetpointer read, which reads the physical address of the entry at each level (PML4, PDP.. etc.). > > Now, what I would like to inquire about is how to identify where this read request for the PTE hits in the memory > hierarchy. In other words, for each step, I would like to know whether this entry was a hit in L1, L2, or L3. So, is > there any field or function/method in the packet that holds this information? If not, how can I get this information? > > Thanks, -- Best regards, Yuan Yao När du har kontakt med oss på Uppsala universitet med e-post så innebär det att vi behandlar dina personuppgifter. För att läsa mer om hur vi gör det kan du läsa här: http://www.uu.se/om-uu/dataskydd-personuppgifter/ E-mailing Uppsala University means that we will process your personal data. For more information on how this is performed, please read here: http://www.uu.se/en/about-uu/data-protection-policy