raw_ostream: while it is generally desirable to do larger writes, it can lead to
inefficient file system buffering if the writes are not a multiple of the desired
buffer size. Avoid this by limiting the large write to a multiple of the buffer
size and copying the remainder into the buffer.
Thanks to Dan for pointing this out.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@127026 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Support/raw_ostream.cpp b/lib/Support/raw_ostream.cpp
index b8839e2..b175d20 100644
--- a/lib/Support/raw_ostream.cpp
+++ b/lib/Support/raw_ostream.cpp
@@ -265,16 +265,20 @@
return write(Ptr, Size);
}
+ size_t NumBytes = OutBufEnd - OutBufCur;
+
// If the buffer is empty at this point we have a string that is larger
- // than the buffer. It's better to write it unbuffered in this case.
+ // than the buffer. Directly write the chunk that is a multiple of the
+ // preferred buffer size and put the remainder in the buffer.
if (BUILTIN_EXPECT(OutBufCur == OutBufStart, false)) {
- write_impl(Ptr, Size);
+ size_t BytesToWrite = Size - (Size % NumBytes);
+ write_impl(Ptr, BytesToWrite);
+ copy_to_buffer(Ptr + BytesToWrite, Size - BytesToWrite);
return *this;
}
// We don't have enough space in the buffer to fit the string in. Insert as
// much as possible, flush and start over with the remainder.
- size_t NumBytes = OutBufEnd - OutBufCur;
copy_to_buffer(Ptr, NumBytes);
flush_nonempty();
return write(Ptr + NumBytes, Size - NumBytes);