Date:   Tue, 12 Mar 2019 17:34:32 +0100
From:   Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
To:     Stanislaw Gruszka <sgruszka@redhat.com>
Cc:     linux-wireless@vger.kernel.org, Felix Fietkau <nbd@nbd.name>
Subject: Re: [RFC 11/12] mt76usb: allocate urb and sg as linear data
Message-ID: <20190312163431.GF2611@localhost.localdomain>
References: <1552403166-3821-1-git-send-email-sgruszka@redhat.com>
 <1552403166-3821-12-git-send-email-sgruszka@redhat.com>
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> Alloc sg table at the end of urb structure. This will increase
> cache usage.
>=20

I am curious, have you observed any performance improvement doing so?

> Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
> ---
>  drivers/net/wireless/mediatek/mt76/usb.c | 20 ++++++++++----------
>  1 file changed, 10 insertions(+), 10 deletions(-)
>=20
> diff --git a/drivers/net/wireless/mediatek/mt76/usb.c b/drivers/net/wirel=
ess/mediatek/mt76/usb.c
> index 0b9f0b5fd37d..dd487f65f44e 100644
> --- a/drivers/net/wireless/mediatek/mt76/usb.c
> +++ b/drivers/net/wireless/mediatek/mt76/usb.c
> @@ -336,19 +336,19 @@ static bool mt76u_check_sg(struct mt76_dev *dev)
>  static int
>  mt76u_urb_alloc(struct mt76_dev *dev, struct mt76_queue_entry *e)
>  {
> -	struct urb *urb;
> +	unsigned int size =3D sizeof(struct urb);
> +
> +	if (dev->usb.sg_en)
> +		size +=3D MT_SG_MAX_SIZE * sizeof(struct scatterlist);
> =20
> -	urb =3D usb_alloc_urb(0, GFP_KERNEL);
> -	if (!urb)
> +	e->urb =3D kzalloc(size, GFP_KERNEL);
> +	if (!e->urb)
>  		return -ENOMEM;
> -	e->urb =3D urb;
> =20
> -	if (dev->usb.sg_en) {
> -		urb->sg =3D devm_kcalloc(dev->dev, MT_SG_MAX_SIZE,
> -				       sizeof(urb->sg), GFP_KERNEL);
> -		if (!urb->sg)
> -			return -ENOMEM;
> -	}
> +	usb_init_urb(e->urb);
> +
> +	if (dev->usb.sg_en)
> +		e->urb->sg =3D (struct scatterlist *)((u8 *)e->urb + sizeof(struct urb=
));

You can avoid u8 cast doing:
(struct scatterlist *)(e->urb + 1)

Regards,
Lorenzo

> =20
>  	return 0;
>  }
> --=20
> 1.9.3
>=20

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