Bump the chunk_size to use CPU more efficiently

The chunk_size used for downloading images was 1KiB for some time. That
is okay for relatively small images but the client side of CPU can be a
bottleneck especially for large images. Bump the default chunk_size from
1KiB to 1MiB so we can use the client side CPU more efficiently.

[1KiB chunk_size - current]

$ time openstack image save IMAGE_689MB --file /dev/null

real    0m16.633s
user    0m12.633s
sys     0m1.365s

-> ~331 Mbps

[1MiB chunk_size - patched]

$ time openstack image save IMAGE_689MB --file /dev/null

real    0m4.896s
user    0m3.361s
sys     0m0.724s

-> ~1,125 Mbps

Story: 2010759
Task: 48044
Change-Id: Ib877d292f8adbf2fa0c51065f2917b3f1e263483

examples/image/download.py

@@ -35,9 +35,9 @@ def download_image_stream(conn):
     with open("myimage.qcow2", "wb") as local_image:
         response = conn.image.download_image(image, stream=True)
 
-        # Read only 1024 bytes of memory at a time until
+        # Read only 1 MiB of memory at a time until
         # all of the image data has been consumed.
-        for chunk in response.iter_content(chunk_size=1024):
+        for chunk in response.iter_content(chunk_size=1024 * 1024):
             # With each chunk, add it to the hash to be computed.
             md5.update(chunk)
 

openstack/cloud/_image.py

@@ -121,7 +121,7 @@ class ImageCloudMixin:
         name_or_id,
         output_path=None,
         output_file=None,
-        chunk_size=1024,
+        chunk_size=1024 * 1024,
     ):
         """Download an image by name or ID
 
@@ -132,7 +132,7 @@ class ImageCloudMixin:
             image data to. Only write() will be called on this object. Either
             this or output_path must be specified
         :param int chunk_size: size in bytes to read from the wire and buffer
-            at one time. Defaults to 1024
+            at one time. Defaults to 1024 * 1024 = 1 MiB
         :returns: When output_path and output_file are not given - the bytes
             comprising the given Image when stream is False, otherwise a
             :class:`requests.Response` instance. When output_path or

openstack/image/_download.py

@@ -25,7 +25,9 @@ def _verify_checksum(md5, checksum):
 
 
 class DownloadMixin:
-    def download(self, session, stream=False, output=None, chunk_size=1024):
+    def download(
+        self, session, stream=False, output=None, chunk_size=1024 * 1024
+    ):
         """Download the data contained in an image"""
         # TODO(briancurtin): This method should probably offload the get
         # operation into another thread or something of that nature.

openstack/image/v1/_proxy.py

@@ -386,7 +386,7 @@ class Proxy(proxy.Proxy):
         image,
         stream=False,
         output=None,
-        chunk_size=1024,
+        chunk_size=1024 * 1024,
     ):
         """Download an image
 
@@ -411,7 +411,7 @@ class Proxy(proxy.Proxy):
             When ``False``, return the entire contents of the response.
         :param output: Either a file object or a path to store data into.
         :param int chunk_size: size in bytes to read from the wire and buffer
-            at one time. Defaults to 1024
+            at one time. Defaults to 1024 * 1024 = 1 MiB
 
         :returns: When output is not given - the bytes comprising the given
             Image when stream is False, otherwise a :class:`requests.Response`

openstack/image/v2/_proxy.py

@@ -776,7 +776,7 @@ class Proxy(proxy.Proxy):
         *,
         stream=False,
         output=None,
-        chunk_size=1024,
+        chunk_size=1024 * 1024,
     ):
         """Download an image
 
@@ -800,7 +800,7 @@ class Proxy(proxy.Proxy):
             When ``False``, return the entire contents of the response.
         :param output: Either a file object or a path to store data into.
         :param int chunk_size: size in bytes to read from the wire and buffer
-            at one time. Defaults to 1024
+            at one time. Defaults to 1024 * 1024 = 1 MiB
 
         :returns: When output is not given - the bytes comprising the given
             Image when stream is False, otherwise a :class:`requests.Response`