netdev - Re: [PATCH 24/25] net/cdc_ncm: Replace tasklet with softirq hrtimer

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Date:   Thu, 31 Aug 2017 15:57:04 +0200
From:   Bjørn Mork <bjorn@...k.no>
To:     Anna-Maria Gleixner <anna-maria@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Christoph Hellwig <hch@....org>, keescook@...omium.org,
        John Stultz <john.stultz@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Oliver Neukum <oliver@...kum.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH 24/25] net/cdc_ncm: Replace tasklet with softirq hrtimer

Anna-Maria Gleixner <anna-maria@...utronix.de> writes:

> From: Thomas Gleixner <tglx@...utronix.de>
>
> The bh tasklet is used in invoke the hrtimer (cdc_ncm_tx_timer_cb) in
> softirq context. This can be also achieved without the tasklet but with
> CLOCK_MONOTONIC_SOFT as hrtimer base.
>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Signed-off-by: Anna-Maria Gleixner <anna-maria@...utronix.de>
> Cc: Oliver Neukum <oliver@...kum.org>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: linux-usb@...r.kernel.org
> Cc: netdev@...r.kernel.org
> ---
>  drivers/net/usb/cdc_ncm.c   |   37 ++++++++++++++++---------------------
>  include/linux/usb/cdc_ncm.h |    2 +-
>  2 files changed, 17 insertions(+), 22 deletions(-)
>
> --- a/drivers/net/usb/cdc_ncm.c
> +++ b/drivers/net/usb/cdc_ncm.c
> @@ -61,7 +61,6 @@ static bool prefer_mbim;
>  module_param(prefer_mbim, bool, S_IRUGO | S_IWUSR);
>  MODULE_PARM_DESC(prefer_mbim, "Prefer MBIM setting on dual NCM/MBIM functions");
>  
> -static void cdc_ncm_txpath_bh(unsigned long param);
>  static void cdc_ncm_tx_timeout_start(struct cdc_ncm_ctx *ctx);
>  static enum hrtimer_restart cdc_ncm_tx_timer_cb(struct hrtimer *hr_timer);
>  static struct usb_driver cdc_ncm_driver;
> @@ -777,10 +776,9 @@ int cdc_ncm_bind_common(struct usbnet *d
>  	if (!ctx)
>  		return -ENOMEM;
>  
> -	hrtimer_init(&ctx->tx_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
> +	hrtimer_init(&ctx->tx_timer, CLOCK_MONOTONIC_SOFT, HRTIMER_MODE_REL);
>  	ctx->tx_timer.function = &cdc_ncm_tx_timer_cb;
> -	ctx->bh.data = (unsigned long)dev;
> -	ctx->bh.func = cdc_ncm_txpath_bh;
> +	ctx->usbnet = dev;
>  	atomic_set(&ctx->stop, 0);
>  	spin_lock_init(&ctx->mtx);
>  
> @@ -967,10 +965,7 @@ void cdc_ncm_unbind(struct usbnet *dev,
>  
>  	atomic_set(&ctx->stop, 1);
>  
> -	if (hrtimer_active(&ctx->tx_timer))
> -		hrtimer_cancel(&ctx->tx_timer);
> -
> -	tasklet_kill(&ctx->bh);
> +	hrtimer_cancel(&ctx->tx_timer);
>  
>  	/* handle devices with combined control and data interface */
>  	if (ctx->control == ctx->data)
> @@ -1348,20 +1343,9 @@ static void cdc_ncm_tx_timeout_start(str
>  				HRTIMER_MODE_REL);
>  }
>  
> -static enum hrtimer_restart cdc_ncm_tx_timer_cb(struct hrtimer *timer)
> +static void cdc_ncm_txpath_bh(struct cdc_ncm_ctx *ctx)
>  {
> -	struct cdc_ncm_ctx *ctx =
> -			container_of(timer, struct cdc_ncm_ctx, tx_timer);
> -
> -	if (!atomic_read(&ctx->stop))
> -		tasklet_schedule(&ctx->bh);
> -	return HRTIMER_NORESTART;
> -}
> -
> -static void cdc_ncm_txpath_bh(unsigned long param)
> -{
> -	struct usbnet *dev = (struct usbnet *)param;
> -	struct cdc_ncm_ctx *ctx = (struct cdc_ncm_ctx *)dev->data[0];
> +	struct usbnet *dev = ctx->usbnet;
>  
>  	spin_lock_bh(&ctx->mtx);
>  	if (ctx->tx_timer_pending != 0) {
> @@ -1379,6 +1363,17 @@ static void cdc_ncm_txpath_bh(unsigned l
>  	}
>  }
>  
> +static enum hrtimer_restart cdc_ncm_tx_timer_cb(struct hrtimer *timer)
> +{
> +	struct cdc_ncm_ctx *ctx =
> +			container_of(timer, struct cdc_ncm_ctx, tx_timer);
> +
> +	if (!atomic_read(&ctx->stop))
> +		cdc_ncm_txpath_bh(ctx);
> +
> +	return HRTIMER_NORESTART;
> +}
> +
>  struct sk_buff *
>  cdc_ncm_tx_fixup(struct usbnet *dev, struct sk_buff *skb, gfp_t flags)
>  {
> --- a/include/linux/usb/cdc_ncm.h
> +++ b/include/linux/usb/cdc_ncm.h
> @@ -92,7 +92,6 @@
>  struct cdc_ncm_ctx {
>  	struct usb_cdc_ncm_ntb_parameters ncm_parm;
>  	struct hrtimer tx_timer;
> -	struct tasklet_struct bh;
>  
>  	const struct usb_cdc_ncm_desc *func_desc;
>  	const struct usb_cdc_mbim_desc *mbim_desc;
> @@ -101,6 +100,7 @@ struct cdc_ncm_ctx {
>  
>  	struct usb_interface *control;
>  	struct usb_interface *data;
> +	struct usbnet *usbnet;
>  
>  	struct sk_buff *tx_curr_skb;
>  	struct sk_buff *tx_rem_skb;




I believe the struct usbnet pointer is redundant.  We already have lots
of pointers back and forth here.  This should work, but is not tested:

	struct usbnet *dev = usb_get_intfdata(ctx->control):




Bjørn