Can begin Results

src/aarch64-linux-flush-dcache/my_shmem.c

@@ -174,6 +174,7 @@ ok:
 	return ret;
 }
 
+// FIXME: bugs in order == 12, alloc pg cnt == 32768
 static vm_fault_t my_shmem_vmops_fault(struct vm_fault *vmf)
 {
 	pr_info("[%s] vm_fault @ 0x%lx (vma + %ld pages).\n",
@@ -184,10 +185,10 @@ static vm_fault_t my_shmem_vmops_fault(struct vm_fault *vmf)
 
 	mutex_lock(&my_shmem_allocs_mtx);
 locked_retry:
-	if (fault_pg_offset < my_shmem_page_count) {
+	if (fault_pg_offset < my_shmem_page_count)
 		// => Already present, remap
 		return __my_shmem_fault_remap(vmf);
-	}
+
 	// else => allocate `1 << order` pages opportunistically...
 	struct my_shmem_alloc *new_alloc_handle = kzalloc(
 		sizeof(struct my_shmem_alloc), GFP_KERNEL
@@ -201,19 +202,23 @@ locked_retry:
 	if (!new_alloc_pg)
 		goto err_alloc_pages;
 
-	// get_page(new_alloc_pg);
 	new_alloc_handle->page = new_alloc_pg;
 	new_alloc_handle->alloc_order = max_contiguous_alloc_order;
 	list_add_tail(&new_alloc_handle->list, &my_shmem_allocs);
 	my_shmem_page_count += ORDER_TO_PAGE_NR(new_alloc_handle->alloc_order);
 	pr_info("[%s] Allocated 1 << %ld pages: 0x%lx - 0x%lx. Current page count: %ld\n",
 		__func__, max_contiguous_alloc_order,
-		page_to_pfn(new_alloc_pg), page_to_pfn(new_alloc_pg) + (1 << max_contiguous_alloc_order),
-		my_shmem_page_count);
+		page_to_pfn(new_alloc_pg),
+		page_to_pfn(new_alloc_pg) + (1 << max_contiguous_alloc_order),
+		my_shmem_page_count
+	);
 
 	goto locked_retry;
 
 err_alloc_pages:
+	pr_err("[%s] Allocation (ord: %ld) failed...\n",
+		__func__, max_contiguous_alloc_order
+	);
 err_kzalloc_handle:
 	ret |= VM_FAULT_OOM;
 err_generic:

tex/draft/mybibfile.bib

@@ -628,3 +628,19 @@
   year={2005},
   publisher={" O'Reilly Media, Inc."}
 }
+
+@misc{Rostedt.Kernelv6.7-ftrace.2023,
+  title={ftrace - Function Tracer},
+  url={https://www.kernel.org/doc/html/v6.7/trace/ftrace.html#dynamic-ftrace},
+  journal={The Linux Kernel documentation},
+  author={Rostedt, Steven},
+  editor={Changbin, Du},
+  year={2023}
+}
+
+@misc{N/A.Kernelv6.7-libbpf.2023,
+  title={libbpf Overview},
+  url={https://www.kernel.org/doc/html/v6.7/bpf/libbpf/libbpf_overview.html},
+  journal={The Linux Kernel documentation},
+  year={2023}
+}

tex/draft/skeleton.tex

@@ -661,7 +661,7 @@ The specifications of \texttt{rose} is listed in table \ref{table:rose}.
 
 \section{Methodology}\label{sec:sw-coherency-method}
 \subsection{Exporting \texttt{dcache\_clean\_poc}}
-As established in subsection \ref{subsec:armv8a-swcoherency}, software cache-coherence maintenance operations (e.g., \texttt{dcache\_[clean|inval]\_poc}) are wrapped behind DMA API function calls and are hence unavailable for direct use in drivers. Moreover, instrumentation of assembly code becomes non-trivial when compared to instrumenting C function symbols, likely due to automatically stripped assembly symbols during kernel linkage. Consequently, it becomes impossible to utilize the existing instrumentation tools available in the Linux kernel (e.g., \texttt{ftrace}) to trace assembly routines.
+As established in subsection \ref{subsec:armv8a-swcoherency}, software cache-coherence maintenance operations (e.g., \texttt{dcache\_[clean|inval]\_poc}) are wrapped behind DMA API function calls and are hence unavailable for direct use in drivers. Moreover, instrumentation of assembly code becomes non-trivial when compared to instrumenting C function symbols, likely due to automatically stripped assembly symbols in C object files. Consequently, it becomes impossible to utilize the existing instrumentation tools available in the Linux kernel (e.g., \texttt{ftrace}) to trace assembly routines.
 
 In order to convert \texttt{dcache\_clean\_poc} to a traceable equivalent, a wrapper function \texttt{\_\_dcache\_clean\_poc} is created as follows:
 \begin{minted}[mathescape, linenos, bgcolor=code-bg]{c}
@@ -988,10 +988,25 @@ $ echo 2 > \
     /sys/module/my_shmem/parameters/max_contiguous_alloc_order
 \end{minted}
 
-Consequently, all allocations occuring after this change will be allocated with a 4-page contiguous granularity.
+Consequently, all allocations occuring after this change will be allocated with a 4-page contiguous granularity. Upon further testing, the maximum value allowed here is 10 (i.e., $2^{10} = 1024$ 4K pages).
+
+\subsection{Instrumentation: \texttt{ftrace} and \texttt{bcc-tools}}
+We use two instrumentation frameworks to evaluate the latency of software-initiated coherency operations. \texttt{ftrace} is the primary kernel tracing mechanism across multiple (supporting) architectures, which supports both \textit{static} tracing of tracepoints and \textit{dynamic} tracing of function symbols:
+\begin{itemize}
+    \item {
+        \textbf{Static} tracepoints describe tracepoints compiled into the Linux kernel. They are defined by kernel programmers and is otherwise known as \textit{event tracing}.
+    }
+    \item {
+        \textbf{Dynamic} \texttt{ftrace} support is enabled by self-modifying the kernel code to replace injected placeholder nop-routines with \texttt{ftrace} infrastructure calls. This allows for function tracing of all function symbols present in C object files created for linkage. \cite{Rostedt.Kernelv6.7-ftrace.2023}
+    }
+\end{itemize}
+
+Because we do not inline \texttt{\_\_dcache\_clean\_poc}, we are able to include its symbol inside compiled C object files and hence expose its internals for dynamic tracing.
+
+\texttt{bcc-tools}, on the other hand, provide an array of handy instrumentation tools that is compiled just-in-time into \textit{BPF} programs and ran inside a in-kernel virtual machine. Description of how BPF programs are parsed and run inside the Linux kernel is documented in the kernel documentations \cite{N/A.Kernelv6.7-libbpf.2023}. The ability of \texttt{bcc}/\texttt{libbpf} programs to interface with both userspace and kernelspace function tracing mechanisms make \texttt{bcc-tools} ideal as a easy tracing interface for both userspace and kernelspace tracing.
 
-\subsection{Instrumentation: \texttt{ftrace} and \textit{eBPF}}
 \subsection{Userspace Programs}
+Finally, two simple userspace programs are written to invoke the corresponding kernelspace callback operations -- namely, allocation and cleaning of kernel buffers for simulating DMA behaviors. To achieve this, it simply \texttt{mmap}s the amount of pages passed in as argument and either reads or writes the entirety of the buffer (which differentiates the two programs). A listing of their logic is at \textcolor{red}{Appendix ???}.
 
 \section{Results}\label{sec:sw-coherency-results}
 \subsection{Controlled Allocation Size; Variable Page Count}