Add a new target.process.memory-cache-line-size to change the size of

lldb's internal memory cache chunks that are read from the remote
system.  For a remote connection that is especially slow, a user may
need to reduce it; reading a 512 byte chunk of memory whenever a
4-byte region is requested may not be the right decision in these
kinds of environments.
<rdar://problem/18175117> 

llvm-svn: 217083

3 files changed, 17 insertions, 2 deletions

diff --git a/lldb/source/Target/Memory.cpp b/lldb/source/Target/Memory.cpp
index b212fcd23a4..0ff1d078bae 100644
--- a/lldb/source/Target/Memory.cpp
+++ b/lldb/source/Target/Memory.cpp
@@ -26,7 +26,7 @@ using namespace lldb_private;
 //----------------------------------------------------------------------
 MemoryCache::MemoryCache(Process &process) :
     m_process (process),
-    m_cache_line_byte_size (512),
+    m_cache_line_byte_size (process.GetMemoryCacheLineSize()),
     m_mutex (Mutex::eMutexTypeRecursive),
     m_cache (),
     m_invalid_ranges ()
@@ -47,6 +47,7 @@ MemoryCache::Clear(bool clear_invalid_ranges)
     m_cache.clear();
     if (clear_invalid_ranges)
         m_invalid_ranges.Clear();
+    m_cache_line_byte_size = m_process.GetMemoryCacheLineSize();
 }
 
 void
diff --git a/lldb/source/Target/Process.cpp b/lldb/source/Target/Process.cpp
index a1049787d82..02f96358433 100644
--- a/lldb/source/Target/Process.cpp
+++ b/lldb/source/Target/Process.cpp
@@ -108,6 +108,7 @@ g_properties[] =
     { "python-os-plugin-path", OptionValue::eTypeFileSpec, false, true, NULL, NULL, "A path to a python OS plug-in module file that contains a OperatingSystemPlugIn class." },
     { "stop-on-sharedlibrary-events" , OptionValue::eTypeBoolean, true, false, NULL, NULL, "If true, stop when a shared library is loaded or unloaded." },
     { "detach-keeps-stopped" , OptionValue::eTypeBoolean, true, false, NULL, NULL, "If true, detach will attempt to keep the process stopped." },
+    { "memory-cache-line-size" , OptionValue::eTypeUInt64, false, 512, NULL, NULL, "The memory cache line size" },
     {  NULL                  , OptionValue::eTypeInvalid, false, 0, NULL, NULL, NULL  }
 };
 
@@ -118,7 +119,8 @@ enum {
     ePropertyUnwindOnErrorInExpressions,
     ePropertyPythonOSPluginPath,
     ePropertyStopOnSharedLibraryEvents,
-    ePropertyDetachKeepsStopped
+    ePropertyDetachKeepsStopped,
+    ePropertyMemCacheLineSize
 };
 
 ProcessProperties::ProcessProperties (bool is_global) :
@@ -148,6 +150,13 @@ ProcessProperties::GetDisableMemoryCache() const
     return m_collection_sp->GetPropertyAtIndexAsBoolean (NULL, idx, g_properties[idx].default_uint_value != 0);
 }
 
+uint64_t
+ProcessProperties::GetMemoryCacheLineSize() const
+{
+    const uint32_t idx = ePropertyMemCacheLineSize;
+    return m_collection_sp->GetPropertyAtIndexAsUInt64 (NULL, idx, g_properties[idx].default_uint_value);
+}
+
 Args
 ProcessProperties::GetExtraStartupCommands () const
 {
diff --git a/lldb/source/Target/Target.cpp b/lldb/source/Target/Target.cpp
index d2d0b509855..946b0e3f280 100644
--- a/lldb/source/Target/Target.cpp
+++ b/lldb/source/Target/Target.cpp
@@ -1436,7 +1436,12 @@ Target::ReadCStringFromMemory (const Address& addr, char *dst, size_t dst_max_le
         Error error;
         addr_t curr_addr = addr.GetLoadAddress(this);
         Address address(addr);
+
+        // We could call m_process_sp->GetMemoryCacheLineSize() but I don't
+        // think this really needs to be tied to the memory cache subsystem's
+        // cache line size, so leave this as a fixed constant.
         const size_t cache_line_size = 512;
+
         size_t bytes_left = dst_max_len - 1;
         char *curr_dst = dst;