Track object inflation time in DfsReaderIoStats

This can help track down poor long tail performance that isn't accounted
for in the readIdxMicros or readBlockMicros metrics.

Change-Id: I701b9cfcc124f4ddb860d1766a11ea3557e604ce
Signed-off-by: Terry Parker <tparker@google.com>

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsReader.java

@@ -757,6 +757,7 @@ public class DfsReader extends ObjectReader implements ObjectReuseAsIs {
 	 */
 	int inflate(DfsPackFile pack, long position, byte[] dstbuf,
 			boolean headerOnly) throws IOException, DataFormatException {
+		long start = System.nanoTime();
 		prepareInflater();
 		pin(pack, position);
 		position += block.setInput(position, inf);
@@ -765,6 +766,7 @@ public class DfsReader extends ObjectReader implements ObjectReuseAsIs {
 			dstoff += n;
 			if (inf.finished() || (headerOnly && dstoff == dstbuf.length)) {
 				stats.inflatedBytes += dstoff;
+				stats.inflationMicros += BlockBasedFile.elapsedMicros(start);
 				return dstoff;
 			} else if (inf.needsInput()) {
 				pin(pack, position);

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsReaderIoStats.java

@@ -85,6 +85,9 @@ public class DfsReaderIoStats {
 		/** Total number of bytes decompressed. */
 		long inflatedBytes;
 
+		/** Total microseconds spent inflating compressed bytes. */
+		long inflationMicros;
+
 		Accumulator() {
 		}
 	}
@@ -186,4 +189,13 @@ public class DfsReaderIoStats {
 	public long getInflatedBytes() {
 		return stats.inflatedBytes;
 	}
+
+	/**
+	 * Get total microseconds spent inflating compressed bytes.
+	 *
+	 * @return total microseconds inflating compressed bytes.
+	 */
+	public long getInflationMicros() {
+		return stats.inflationMicros;
+	}
 }