netdev - Re: [EXT] [PATCH V2] bnx2x: Prevent ptp_task to be rescheduled indefinitely

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Date:   Tue, 25 Jun 2019 09:55:30 -0300
From:   Guilherme Piccoli <gpiccoli@...onical.com>
To:     Sudarsana Reddy Kalluru <skalluru@...vell.com>
Cc:     GR-everest-linux-l2 <GR-everest-linux-l2@...vell.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Ariel Elior <aelior@...vell.com>,
        "jay.vosburgh@...onical.com" <jay.vosburgh@...onical.com>
Subject: Re: [EXT] [PATCH V2] bnx2x: Prevent ptp_task to be rescheduled indefinitely

On Tue, Jun 25, 2019 at 1:02 AM Sudarsana Reddy Kalluru
<skalluru@...vell.com> wrote:
>
> Thanks for your changes and time on this. In general time-latching happens in couple or more milliseconds (even in some 100s of usec) under the normal traffic conditions. With this approach, there's a possibility that every packet has to wait for atleast 50ms for the timestamping. This in turn affects the wait-queue (of packets to be timestamped) at hardware as next TS recording happens only after the register is freed/read. And also, it incurs some latency for the ptp applications.
>
> PTP thread is consuming time may be due to the debug messages in this error path, which you are planning address already (thanks!!).
>    "Also, I've dropped the PTP "outstanding, etc" messages to debug-level, they're quite flooding my log.
> Do you see cpu hog even after removing this message? In such case we may need to think of other alternatives such as sleep for 1 ms.
> Just for the info, the approach continuous-poll-for-timestamp() is used ixgbe driver (ixgbe_ptp_tx_hwtstamp_work()) as well.
>

Thanks again for the good insights Sudarsana! I'll do some experiments
dropping all messages and checking
if the ptp thread is still consuming a lot of CPU (I believe so). In
this case, I'll rework the approach by starting
the delays in 1ms to avoid impacting the HW wait-queue and causing
delays in ptp applications.

Cheers,


Guilherme