[gem5-users] TLB statistics riscv

[Mirco Mannino via gem5-users]

Hi all,

I am looking at how the TLB is implemented (riscv ISA). In particular, I 
am interested in TLB statistics.

I noticed that, in the TLB::lokup method 
(https://github.com/gem5/gem5/blob/stable/src/arch/riscv/tlb.cc#L109), 
there is an input argument (i.e., hidden) which determines whether the 
TLB lookup should or should not update TLB statistics.

In the TLB::doTranslate 
(https://github.com/gem5/gem5/blob/stable/src/arch/riscv/tlb.cc#L278) 
method, the first lookup updates TLB statistics (i.e., hidden=false).
After a TLB miss, the page walker is invoked and the TLB is looked up 
again in the same way.

The source code is the following:

TlbEntry *e = lookup(vaddr, satp.asid, mode, *false*);
    if (!e) {
        Fault fault = walker->start(tc, translation, req, mode);
        if (translation != nullptr || fault != NoFault) {
            // This gets ignored in atomic mode.
            delayed = true;
            return fault;
        }
        e = lookup(vaddr, satp.asid, mode, *false*);
        assert(e != nullptr);
    }


I was wondering if this behavior is correct.
Shouldn't we just count the first TLB miss and use the second TLB access 
only to check the correctness of the page walker? Also because surely 
the second TLB lookup will definitely result in a TLB hit, otherwise the 
simulation is interrupted by an assert.

Thanks in advance,
Mirco_______________________________________________
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