clarify when to use '--single-thread' with '--patch-from'

Using '--single-thread' with '--patch-from' on compression levels above 15 will lead to significantly worse compression ratios.

Corrected the man page not suggest anymore to do this.

diff --git a/programs/zstd.1.md b/programs/zstd.1.md
index fcbfb457301a052382ee13d8bcaa29daded82a73..5188be6a51508b5c7fa4c13622b1809a0199b184 100644 (file)
--- a/programs/zstd.1.md
+++ b/programs/zstd.1.md
@@ -174,8 +174,10 @@ the last one takes effect.
         (_fileLog_ being the _windowLog_ required to cover the whole file). You
         can also manually force it.
 
-    Note: for all levels, you can use `--patch-from` in `--single-thread` mode
-        to improve compression ratio at the cost of speed.
+    Note: up to level 15, you can use `--patch-from` in `--single-thread` mode
+        to improve compression ratio marginally at the cost of speed. Using
+        '--single-thread' above level 15  will lead to lower compression
+        ratios.
 
     Note: for level 19, you can get increased compression ratio at the cost
         of speed by specifying `--zstd=targetLength=` to be something large