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Date: Wed, 9 Nov 2022 11:23:43 +0000 From: Haozhe Chang (常浩哲) <Haozhe.Chang@...iatek.com> To: "loic.poulain@...aro.org" <loic.poulain@...aro.org> CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "linux-mediatek@...ts.infradead.org" <linux-mediatek@...ts.infradead.org>, "linuxwwan@...el.com" <linuxwwan@...el.com>, "m.chetan.kumar@...ux.intel.com" <m.chetan.kumar@...ux.intel.com>, Hua Yang (杨华) <Hua.Yang@...iatek.com>, Haijun Liu (刘海军) <haijun.liu@...iatek.com>, Haozhe Chang (常浩哲) <Haozhe.Chang@...iatek.com>, "chiranjeevi.rapolu@...ux.intel.com" <chiranjeevi.rapolu@...ux.intel.com>, "ryazanov.s.a@...il.com" <ryazanov.s.a@...il.com>, "kuba@...nel.org" <kuba@...nel.org>, Xiayu Zhang (张夏宇) <Xiayu.Zhang@...iatek.com>, "johannes@...solutions.net" <johannes@...solutions.net>, "chandrashekar.devegowda@...el.com" <chandrashekar.devegowda@...el.com>, "edumazet@...gle.com" <edumazet@...gle.com>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>, "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>, "pabeni@...hat.com" <pabeni@...hat.com>, "matthias.bgg@...il.com" <matthias.bgg@...il.com>, "ricardo.martinez@...ux.intel.com" <ricardo.martinez@...ux.intel.com>, "davem@...emloft.net" <davem@...emloft.net>, Lambert Wang (王伟) <Lambert.Wang@...iatek.com>, "srv_heupstream@...iatek.com" <srv_heupstream@...iatek.com> Subject: Re: [PATCH v2] wwan: core: Support slicing in port TX flow of WWAN subsystem Hi Loic On Tue, 2022-11-08 at 13:14 +0100, Loic Poulain wrote: > Hi Haozhe, > > On Tue, 8 Nov 2022 at 11:54, <haozhe.chang@...iatek.com> wrote: > > > > From: haozhe chang <haozhe.chang@...iatek.com> > > > > wwan_port_fops_write inputs the SKB parameter to the TX callback of > > the WWAN device driver. However, the WWAN device (e.g., t7xx) may > > have an MTU less than the size of SKB, causing the TX buffer to be > > sliced and copied once more in the WWAN device driver. > > > > This patch implements the slicing in the WWAN subsystem and gives > > the WWAN devices driver the option to slice(by chunk) or not. By > > doing so, the additional memory copy is reduced. > > > > Meanwhile, this patch gives WWAN devices driver the option to > > reserve > > headroom in SKB for the device-specific metadata. > > > > Signed-off-by: haozhe chang <haozhe.chang@...iatek.com> > > > > --- > > Changes in v2 > > -send fragments to device driver by skb frag_list. > > --- > > drivers/net/wwan/t7xx/t7xx_port_wwan.c | 42 ++++++++++------- > > drivers/net/wwan/wwan_core.c | 65 ++++++++++++++++++++ > > ------ > > include/linux/wwan.h | 5 +- > > 3 files changed, 80 insertions(+), 32 deletions(-) > > > > diff --git a/drivers/net/wwan/t7xx/t7xx_port_wwan.c > > b/drivers/net/wwan/t7xx/t7xx_port_wwan.c > > index 33931bfd78fd..74fa58575d5a 100644 > > --- a/drivers/net/wwan/t7xx/t7xx_port_wwan.c > > +++ b/drivers/net/wwan/t7xx/t7xx_port_wwan.c > > @@ -54,13 +54,13 @@ static void t7xx_port_ctrl_stop(struct > > wwan_port *port) > > [...] > > static const struct wwan_port_ops wwan_ops = { > > .start = t7xx_port_ctrl_start, > > .stop = t7xx_port_ctrl_stop, > > .tx = t7xx_port_ctrl_tx, > > + .needed_headroom = t7xx_port_tx_headroom, > > + .tx_chunk_len = t7xx_port_tx_chunk_len, > > Can you replace 'chunk' with 'frag' everywhere? > OK > > }; > > > > static int t7xx_port_wwan_init(struct t7xx_port *port) > > diff --git a/drivers/net/wwan/wwan_core.c > > b/drivers/net/wwan/wwan_core.c > > index 62e9f7d6c9fe..ed78471f9e38 100644 > > --- a/drivers/net/wwan/wwan_core.c > > +++ b/drivers/net/wwan/wwan_core.c > > @@ -20,7 +20,7 @@ > > #include <uapi/linux/wwan.h> > > > > /* Maximum number of minors in use */ > > -#define WWAN_MAX_MINORS (1 << MINORBITS) > > +#define WWAN_MAX_MINORS BIT(MINORBITS) > > > > static DEFINE_MUTEX(wwan_register_lock); /* WWAN device > > create|remove lock */ > > static DEFINE_IDA(minors); /* minors for WWAN port chardevs */ > > @@ -67,6 +67,8 @@ struct wwan_device { > > * @rxq: Buffer inbound queue > > * @waitqueue: The waitqueue for port fops (read/write/poll) > > * @data_lock: Port specific data access serialization > > + * @headroom_len: SKB reserved headroom size > > + * @chunk_len: Chunk len to split packet > > * @at_data: AT port specific data > > */ > > struct wwan_port { > > @@ -79,6 +81,8 @@ struct wwan_port { > > struct sk_buff_head rxq; > > wait_queue_head_t waitqueue; > > struct mutex data_lock; /* Port specific data access > > serialization */ > > + size_t headroom_len; > > + size_t chunk_len; > > union { > > struct { > > struct ktermios termios; > > @@ -550,8 +554,13 @@ static int wwan_port_op_start(struct wwan_port > > *port) > > } > > > > /* If port is already started, don't start again */ > > - if (!port->start_count) > > + if (!port->start_count) { > > ret = port->ops->start(port); > > + if (port->ops->tx_chunk_len) > > + port->chunk_len = port->ops- > > >tx_chunk_len(port); > > So, maybe frag len and headroom should be parameters of > wwan_create_port() instead of port ops, as we really need this info > only once. > If frag_len and headroom are added, wwan_create_port will have 6 parameters, is it too much? And for similar requirements in the future, it may be difficult to add more parameters. Is it a good solution to provide wwan_port_set_frag_len and wwan_port_set_headroom_len to the device driver? if so, the device driver has a chance to modify the wwan port's field after calling wwan_create_port. > > + if (port->ops->needed_headroom) > > + port->headroom_len = port->ops- > > >needed_headroom(port); > > + } > > > > if (!ret) > > port->start_count++; > > @@ -698,30 +707,56 @@ static ssize_t wwan_port_fops_read(struct > > file *filp, char __user *buf, > > static ssize_t wwan_port_fops_write(struct file *filp, const char > > __user *buf, > > size_t count, loff_t *offp) > > { > > + size_t len, chunk_len, offset, allowed_chunk_len; > > + struct sk_buff *skb, *head = NULL, *tail = NULL; > > struct wwan_port *port = filp->private_data; > > - struct sk_buff *skb; > > int ret; > > > > ret = wwan_wait_tx(port, !!(filp->f_flags & O_NONBLOCK)); > > if (ret) > > return ret; > > > > - skb = alloc_skb(count, GFP_KERNEL); > > - if (!skb) > > - return -ENOMEM; > > + allowed_chunk_len = port->chunk_len ? port->chunk_len : > > count; > > I would suggest making port->chunk_len (frag_len) always valid, by > setting it to -1 (MAX size_t) when creating a port without frag_len > requirement. > Ok, it will help to reduce some code. > > + for (offset = 0; offset < count; offset += chunk_len) { > > + chunk_len = min(count - offset, allowed_chunk_len); > > + len = chunk_len + port->headroom_len; > > + skb = alloc_skb(len, GFP_KERNEL); > > That works but would prefer a simpler solution like: > do { > len = min(port->frag_len, remain); > skb = alloc_skb(len + port->needed_headroom; GFP_KERNEL); > [...] > copy_from_user(skb_put(skb, len), buf + count - remain) > } while ((remain -= len)); > May I know if the suggestion is because "while" is more efficient than "for", or is it more readable? > > + if (!skb) { > > + ret = -ENOMEM; > > + goto freeskb; > > + } > > + skb_reserve(skb, port->headroom_len); > > + > > + if (!head) { > > + head = skb; > > + } else if (!tail) { > > + skb_shinfo(head)->frag_list = skb; > > + tail = skb; > > + } else { > > + tail->next = skb; > > + tail = skb; > > + } > > > > - if (copy_from_user(skb_put(skb, count), buf, count)) { > > - kfree_skb(skb); > > - return -EFAULT; > > - } > > + if (copy_from_user(skb_put(skb, chunk_len), buf + > > offset, chunk_len)) { > > + ret = -EFAULT; > > + goto freeskb; > > + } > > > > - ret = wwan_port_op_tx(port, skb, !!(filp->f_flags & > > O_NONBLOCK)); > > - if (ret) { > > - kfree_skb(skb); > > - return ret; > > + if (skb != head) { > > + head->data_len += skb->len; > > + head->len += skb->len; > > + head->truesize += skb->truesize; > > + } > > } > > > > - return count; > > + if (head) { > > How head can be null here? > if the parameter "count" is 0, the for loop will not be executed. > > + ret = wwan_port_op_tx(port, head, !!(filp->f_flags > > & O_NONBLOCK)); > > + if (!ret) > > + return count; > > + } > > +freeskb: > > + kfree_skb(head); > > + return ret; > > } > > > > static __poll_t wwan_port_fops_poll(struct file *filp, poll_table > > *wait) > > diff --git a/include/linux/wwan.h b/include/linux/wwan.h > > index 5ce2acf444fb..bdeeef59bbfd 100644 > > --- a/include/linux/wwan.h > > +++ b/include/linux/wwan.h > > @@ -46,6 +46,8 @@ struct wwan_port; > > * @tx: Non-blocking routine that sends WWAN port protocol data to > > the device. > > * @tx_blocking: Optional blocking routine that sends WWAN port > > protocol data > > * to the device. > > + * @needed_headroom: Optional routine that sets reserve headroom > > of skb. > > + * @tx_chunk_len: Optional routine that sets chunk len to split. > > * @tx_poll: Optional routine that sets additional TX poll flags. > > * > > * The wwan_port_ops structure contains a list of low-level > > operations > > @@ -58,6 +60,8 @@ struct wwan_port_ops { > > > > /* Optional operations */ > > int (*tx_blocking)(struct wwan_port *port, struct sk_buff > > *skb); > > + size_t (*needed_headroom)(struct wwan_port *port); > > + size_t (*tx_chunk_len)(struct wwan_port *port); > > As said above, maybe move that as variables, or parameter of > wwan_create_port. > > Regards, > Loic
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