linux-kernel - Re: [PATCH] usb: typec: tcpm: Move to high priority workqueue for processing events

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Message-ID: <20200714060520.GB657428@kroah.com>
Date:   Tue, 14 Jul 2020 08:05:20 +0200
From:   reg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Badhri Jagan Sridharan <badhri@...gle.com>
Cc:     Guenter Roeck <linux@...ck-us.net>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb: typec: tcpm: Move to high priority workqueue for
 processing events

On Mon, Jul 13, 2020 at 01:43:00PM -0700, Badhri Jagan Sridharan wrote:
> "tReceiverResponse 15 ms Section 6.6.2
> The receiver of a Message requiring a response Shall respond
> within tReceiverResponse in order to ensure that the
> sender’s SenderResponseTimer does not expire."
> 
> When the cpu complex is busy running other lower priority
> work items, TCPM's work queue sometimes does not get scheduled
> on time to meet the above requirement from the spec.
> Elevating the TCPM's work queue to higher priority allows
> TCPM to meet tReceiverResponse in a busy system.
> 
> Signed-off-by: Badhri Jagan Sridharan <badhri@...gle.com>
> ---
>  drivers/usb/typec/tcpm/tcpm.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
> index 82b19ebd7838e0..088b6f1fa1ff89 100644
> --- a/drivers/usb/typec/tcpm/tcpm.c
> +++ b/drivers/usb/typec/tcpm/tcpm.c
> @@ -4747,7 +4747,7 @@ struct tcpm_port *tcpm_register_port(struct device *dev, struct tcpc_dev *tcpc)
>  	mutex_init(&port->lock);
>  	mutex_init(&port->swap_lock);
>  
> -	port->wq = create_singlethread_workqueue(dev_name(dev));
> +	port->wq = alloc_ordered_workqueue("%s", WQ_HIGHPRI, dev_name(dev));

How are you "guaranteeing" that this is really going to change anything
on a highly loaded machine?

Yes, it might make things better, but if you have a hard deadline like
this, you need to do things a bit differently to always ensure that you
meet it.  I do not think this change is that fix, do you?

thanks,

greg k-h