netdev - Fw: [Bug 206919] New: Very bad performance of sendto function

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Date:   Mon, 23 Mar 2020 09:59:18 -0700
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     netdev@...r.kernel.org
Subject: Fw: [Bug 206919] New: Very bad performance of sendto function

There maybe something here but probably not.

Begin forwarded message:

Date: Sun, 22 Mar 2020 11:22:46 +0000
From: bugzilla-daemon@...zilla.kernel.org
To: stephen@...workplumber.org
Subject: [Bug 206919] New: Very bad performance of sendto function

https://bugzilla.kernel.org/show_bug.cgi?id=206919

            Bug ID: 206919
           Summary: Very bad performance of sendto function
           Product: Networking
           Version: 2.5
    Kernel Version: 5.4.13
          Hardware: All
                OS: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: Other
          Assignee: stephen@...workplumber.org
          Reporter: bernat.arlandis@...il.com
        Regression: No

Created attachment 288007
  --> https://bugzilla.kernel.org/attachment.cgi?id=288007&action=edit  
Sysprof capture file

Hi,

I have a case where the sendto function is slowing down the software I'm trying
to use. Sysprof capture file attached.

It's probably being called at a high frequency and the __netlink_dump_start
function spends a lot of time in the mutex lock, then also in the netlink_dump
call.

This is causing the threads calling the function to stall. At least this is my
interpretation of the profiling session.

I don't have any knowledge about the way networking code works. I'd like to
know if the flaw is in the user-space software or in the kernel. Can I provide
any more info or do some test to help determine what's happening? I'd like to
help fix it.

My NIC: Intel Corporation I211 Gigabit Network Connection (rev 03)

My system: Debian 10 with kernel 5.4.13.

Thanks.

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