From 0d84909d667bf3ebd49db2ba87af759d1f326aba Mon Sep 17 00:00:00 2001
From: Sandeep Dhavale <dhavale@google.com>
Date: Fri, 27 Sep 2024 13:37:18 -0700
Subject: [PATCH] libsnapshot: Use words for xor ops

Use words instead of doing xor byte-by-byte for the entire buffer.
Profiling this with unittest, I can see the xor ops is much faster.

Also handle the word size appropriately for 32bit and 64bit platforms.

simpleperf shows that ProcessXorOp() is atleast 30% faster.
Similar improvement is seen for ProcessXorData().

Test: snapuserd_test
Bug: 369905394
Change-Id: I0bd8586f7fc1bf184f19320667b8195b07f9cdf2
Signed-off-by: Sandeep Dhavale <dhavale@google.com>
---
 .../snapuserd/user-space-merge/read_worker.cpp       | 11 ++++++++---
 .../user-space-merge/snapuserd_readahead.cpp         | 12 +++++++-----
 2 files changed, 15 insertions(+), 8 deletions(-)

diff --git a/fs_mgr/libsnapshot/snapuserd/user-space-merge/read_worker.cpp b/fs_mgr/libsnapshot/snapuserd/user-space-merge/read_worker.cpp
index ef311d475..33767d654 100644
--- a/fs_mgr/libsnapshot/snapuserd/user-space-merge/read_worker.cpp
+++ b/fs_mgr/libsnapshot/snapuserd/user-space-merge/read_worker.cpp
@@ -104,6 +104,8 @@ bool ReadWorker::ProcessCopyOp(const CowOperation* cow_op, void* buffer) {
 }
 
 bool ReadWorker::ProcessXorOp(const CowOperation* cow_op, void* buffer) {
+    using WordType = std::conditional_t<sizeof(void*) == sizeof(uint64_t), uint64_t, uint32_t>;
+
     if (!ReadFromSourceDevice(cow_op, buffer)) {
         return false;
     }
@@ -120,9 +122,12 @@ bool ReadWorker::ProcessXorOp(const CowOperation* cow_op, void* buffer) {
         return false;
     }
 
-    auto xor_out = reinterpret_cast<uint8_t*>(buffer);
-    for (size_t i = 0; i < BLOCK_SZ; i++) {
-        xor_out[i] ^= xor_buffer_[i];
+    auto xor_in = reinterpret_cast<const WordType*>(xor_buffer_.data());
+    auto xor_out = reinterpret_cast<WordType*>(buffer);
+    auto num_words = BLOCK_SZ / sizeof(WordType);
+
+    for (auto i = 0; i < num_words; i++) {
+        xor_out[i] ^= xor_in[i];
     }
     return true;
 }
diff --git a/fs_mgr/libsnapshot/snapuserd/user-space-merge/snapuserd_readahead.cpp b/fs_mgr/libsnapshot/snapuserd/user-space-merge/snapuserd_readahead.cpp
index 6b1ed0cd7..9a1d441c4 100644
--- a/fs_mgr/libsnapshot/snapuserd/user-space-merge/snapuserd_readahead.cpp
+++ b/fs_mgr/libsnapshot/snapuserd/user-space-merge/snapuserd_readahead.cpp
@@ -458,6 +458,7 @@ bool ReadAhead::ReapIoCompletions(int pending_ios_to_complete) {
 void ReadAhead::ProcessXorData(size_t& block_xor_index, size_t& xor_index,
                                std::vector<const CowOperation*>& xor_op_vec, void* buffer,
                                loff_t& buffer_offset) {
+    using WordType = std::conditional_t<sizeof(void*) == sizeof(uint64_t), uint64_t, uint32_t>;
     loff_t xor_buf_offset = 0;
 
     while (block_xor_index < blocks_.size()) {
@@ -470,13 +471,14 @@ void ReadAhead::ProcessXorData(size_t& block_xor_index, size_t& xor_index,
             // Check if this block is an XOR op
             if (xor_op->new_block == new_block) {
                 // Pointer to the data read from base device
-                uint8_t* buffer = reinterpret_cast<uint8_t*>(bufptr);
+                auto buffer_words = reinterpret_cast<WordType*>(bufptr);
                 // Get the xor'ed data read from COW device
-                uint8_t* xor_data = reinterpret_cast<uint8_t*>((char*)bufsink_.GetPayloadBufPtr() +
-                                                               xor_buf_offset);
+                auto xor_data_words = reinterpret_cast<WordType*>(
+                        (char*)bufsink_.GetPayloadBufPtr() + xor_buf_offset);
+                auto num_words = BLOCK_SZ / sizeof(WordType);
 
-                for (size_t byte_offset = 0; byte_offset < BLOCK_SZ; byte_offset++) {
-                    buffer[byte_offset] ^= xor_data[byte_offset];
+                for (auto i = 0; i < num_words; i++) {
+                    buffer_words[i] ^= xor_data_words[i];
                 }
 
                 // Move to next XOR op