netdev - Re: [PATCH 1/2] mwifiex: Use non-posted PCI register writes

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Date:   Wed, 1 Sep 2021 14:07:43 -0700
From:   Brian Norris <briannorris@...omium.org>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Jonas Dreßler <verdre@...d.nl>,
        Amitkumar Karwar <amitkarwar@...il.com>,
        Ganapathi Bhat <ganapathi017@...il.com>,
        Xinming Hu <huxinming820@...il.com>,
        Kalle Valo <kvalo@...eaurora.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Tsuchiya Yuto <kitakar@...il.com>,
        linux-wireless <linux-wireless@...r.kernel.org>,
        "<netdev@...r.kernel.org>" <netdev@...r.kernel.org>,
        Linux Kernel <linux-kernel@...r.kernel.org>,
        linux-pci <linux-pci@...r.kernel.org>,
        Maximilian Luz <luzmaximilian@...il.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Pali Rohár <pali@...nel.org>
Subject: Re: [PATCH 1/2] mwifiex: Use non-posted PCI register writes

Apologies for the brain-dead mailer. I forget that I should only reply
via web when I _want_ text wrapping:

On Wed, Sep 01, 2021 at 02:04:04PM -0700, Brian Norris wrote:
> (b) latency spikes to ~6ms:
> # trace-cmd record -p function_graph -O funcgraph-abstime -l
> mwifiex_pm_wakeup_card
> # trace-cmd report
>    kworker/u13:0-199   [003]   348.987306: funcgraph_entry:      #
> 6219.500 us |  mwifiex_pm_wakeup_card();
>    kworker/u13:0-199   [003]   349.316312: funcgraph_entry:      #
> 6267.625 us |  mwifiex_pm_wakeup_card();
>    kworker/u13:3-4057  [001]   352.238530: funcgraph_entry:      #
> 6184.250 us |  mwifiex_pm_wakeup_card();
>    kworker/u13:0-199   [002]   356.626366: funcgraph_entry:      #
> 6553.166 us |  mwifiex_pm_wakeup_card();
>    kworker/u13:3-4057  [002]   356.709389: funcgraph_entry:      #
> 6212.500 us |  mwifiex_pm_wakeup_card();
>    kworker/u13:3-4057  [002]   356.847215: funcgraph_entry:      #
> 6230.292 us |  mwifiex_pm_wakeup_card();
>    kworker/u13:3-4057  [000]   356.897576: funcgraph_entry:      #
> 6451.667 us |  mwifiex_pm_wakeup_card();
>    kworker/u13:0-199   [004]   357.175025: funcgraph_entry:      #
> 6204.042 us |  mwifiex_pm_wakeup_card();
> 
> whereas it used to look more like:
> 
>    kworker/u13:1-173   [005]   212.230542: funcgraph_entry:
> 7.000 us   |  mwifiex_pm_wakeup_card();
>    kworker/u13:3-1768  [005]   213.886063: funcgraph_entry:
> 9.334 us   |  mwifiex_pm_wakeup_card();
>    kworker/u13:3-1768  [002]   214.473273: funcgraph_entry:      +
> 11.375 us  |  mwifiex_pm_wakeup_card();
>    kworker/u13:3-1768  [005]   214.530705: funcgraph_entry:
> 5.542 us   |  mwifiex_pm_wakeup_card();
>    kworker/u13:1-173   [002]   215.050168: funcgraph_entry:      +
> 13.125 us  |  mwifiex_pm_wakeup_card();
>    kworker/u13:1-173   [002]   215.106492: funcgraph_entry:      +
> 11.959 us  |  mwifiex_pm_wakeup_card();
>    kworker/u13:3-1768  [005]   215.484807: funcgraph_entry:
> 8.459 us   |  mwifiex_pm_wakeup_card();
>    kworker/u13:1-173   [003]   215.515238: funcgraph_entry:      +
> 15.166 us  |  mwifiex_pm_wakeup_card();
>    kworker/u13:3-1768  [001]   217.175691: funcgraph_entry:      +
> 11.083 us  |  mwifiex_pm_wakeup_card();

That should read:

# trace-cmd record -p function_graph -O funcgraph-abstime -l mwifiex_pm_wakeup_card
# trace-cmd report
   kworker/u13:0-199   [003]   348.987306: funcgraph_entry:      # 6219.500 us |  mwifiex_pm_wakeup_card();
   kworker/u13:0-199   [003]   349.316312: funcgraph_entry:      # 6267.625 us |  mwifiex_pm_wakeup_card();
   kworker/u13:3-4057  [001]   352.238530: funcgraph_entry:      # 6184.250 us |  mwifiex_pm_wakeup_card();
   kworker/u13:0-199   [002]   356.626366: funcgraph_entry:      # 6553.166 us |  mwifiex_pm_wakeup_card();
   kworker/u13:3-4057  [002]   356.709389: funcgraph_entry:      # 6212.500 us |  mwifiex_pm_wakeup_card();
   kworker/u13:3-4057  [002]   356.847215: funcgraph_entry:      # 6230.292 us |  mwifiex_pm_wakeup_card();
   kworker/u13:3-4057  [000]   356.897576: funcgraph_entry:      # 6451.667 us |  mwifiex_pm_wakeup_card();
   kworker/u13:0-199   [004]   357.175025: funcgraph_entry:      # 6204.042 us |  mwifiex_pm_wakeup_card();

vs.

   kworker/u13:1-173   [005]   212.230542: funcgraph_entry:        7.000 us   |  mwifiex_pm_wakeup_card();
   kworker/u13:3-1768  [005]   213.886063: funcgraph_entry:        9.334 us   |  mwifiex_pm_wakeup_card();
   kworker/u13:3-1768  [002]   214.473273: funcgraph_entry:      + 11.375 us  |  mwifiex_pm_wakeup_card();
   kworker/u13:3-1768  [005]   214.530705: funcgraph_entry:        5.542 us   |  mwifiex_pm_wakeup_card();
   kworker/u13:1-173   [002]   215.050168: funcgraph_entry:      + 13.125 us  |  mwifiex_pm_wakeup_card();
   kworker/u13:1-173   [002]   215.106492: funcgraph_entry:      + 11.959 us  |  mwifiex_pm_wakeup_card();
   kworker/u13:3-1768  [005]   215.484807: funcgraph_entry:        8.459 us   |  mwifiex_pm_wakeup_card();
   kworker/u13:1-173   [003]   215.515238: funcgraph_entry:      + 15.166 us  |  mwifiex_pm_wakeup_card();
   kworker/u13:3-1768  [001]   217.175691: funcgraph_entry:      + 11.083 us  |  mwifiex_pm_wakeup_card();

Brian