[Libguestfs] [PATCH] v2v: rhv-upload: Disable Nagle algorithm

[Richard W.M. Jones]

On Fri, Jun 15, 2018 at 10:57:32PM +0300, Nir Soffer wrote:
> When sending a PUT request, the http header may be sent in the first
> packet when calling con.endheaders(). When we send the first chunk, the
> kernel may delay the send because the header packet was not acked yet.
> 
> We have seen PUT requests delayed by 40 milliseconds on the server side
> during virt-v2v upload to ovirt. Here is example log from current RHEL
> virt-v2v version, uploading to RHV 4.2.3:
> 
> 2018-06-12 17:04:01,750 INFO    (Thread-2) [images] Writing 52736 bytes
> at offset 0 flush False to /path/to/image for ticket
> 374bec27-930d-4097-8e41-e4bc23324eb0
> 
> 2018-06-12 17:04:01,790 INFO    (Thread-2) [directio] Operation stats:
> <Clock(total=0.04, read=0.04, write=0.00)>
> 
> The server spent 40 milliseconds reading 52736 bytes form
> rhv_upload_plugin running on the same host.
> 
> This issue was fixed in python 3.5 by using the TCP_NO_DELAY option
> after connecting[1]. I backported this change from python 3.5.
> 
> I tested the same change using imageio example upload script. With this
> change and with optimized PATCH requests, upload time of 4G sparse image
> was reduced from 7 minutes to 1 minute.
> 
> See this ovirt patch for more details:
> https://gerrit.ovirt.org/#/c/92276/
> 
> This change is needed only for python 2.
> 
> [1] https://bugs.python.org/issue23302
> ---
>  v2v/rhv-upload-plugin.py | 14 +++++++++++++-
>  1 file changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/v2v/rhv-upload-plugin.py b/v2v/rhv-upload-plugin.py
> index ed99cc7a9..f8cd37e9f 100644
> --- a/v2v/rhv-upload-plugin.py
> +++ b/v2v/rhv-upload-plugin.py
> @@ -23,7 +23,7 @@ import ssl
>  import sys
>  import time
>  
> -from http.client import HTTPSConnection
> +from http.client import HTTPSConnection as _HTTPSConnection
>  from urllib.parse import urlparse
>  
>  import ovirtsdk4 as sdk
> @@ -38,6 +38,18 @@ timeout = 5*60
>  # is no formal API here.
>  params = None
>  
> +class HTTPSConnection(_HTTPSConnection):
> +    def connect(self):
> +        """
> +        Using TCP_NO_DELAY avoids delays when sending small payload, such as
> +        ovirt PATCH requests.
> +
> +        This issue was fixed in python 3.5, see:
> +        https://bugs.python.org/issue23302
> +        """
> +        _HTTPSConnection.connect(self)
> +        self.sock.setsockopt(socket.IPPROTO_TCP, socket.TCP_NODELAY, 1)
> +
>  def config(key, value):
>      global params
>  

ACK.

Note that we only need this downstream (in RHEL >= 7.6).  I have filed
a bug to include this patch:

  https://bugzilla.redhat.com/show_bug.cgi?id=1591960

In Fedora and RHEL >= 8 we're Python 3.6+ only, so the bug shouldn't
affect us there.

Thanks,

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
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