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Date: Tue, 6 Dec 2022 22:05:40 -0600
From: Bjorn Andersson <andersson@...nel.org>
To: Piotr Wojtaszczyk <piotr.wojtaszczyk@...esys.com>
Cc: Mathieu Poirier <mathieu.poirier@...aro.org>,
linux-remoteproc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rpmsg: char: Use preallocated SKBs.
On Tue, Dec 06, 2022 at 10:38:41AM +0100, Piotr Wojtaszczyk wrote:
> On a message reception copy the message to a SKB taken from preallocated
> pool instead of allocating a new SKB each time.
> During high rpmsg traffic this reduces consumed CPU time noticeably.
>
> Signed-off-by: Piotr Wojtaszczyk <piotr.wojtaszczyk@...esys.com>
> ---
> drivers/rpmsg/rpmsg_char.c | 46 +++++++++++++++++++++++++++++---
> drivers/rpmsg/rpmsg_internal.h | 21 +++++++++++++++
> drivers/rpmsg/virtio_rpmsg_bus.c | 21 ---------------
> 3 files changed, 64 insertions(+), 24 deletions(-)
>
> diff --git a/drivers/rpmsg/rpmsg_char.c b/drivers/rpmsg/rpmsg_char.c
> index 3e0b8f3496ed..51b1b077687e 100644
> --- a/drivers/rpmsg/rpmsg_char.c
> +++ b/drivers/rpmsg/rpmsg_char.c
> @@ -66,10 +66,37 @@ struct rpmsg_eptdev {
>
> spinlock_t queue_lock;
> struct sk_buff_head queue;
> + struct sk_buff_head skb_pool;
> wait_queue_head_t readq;
>
> };
>
> +static inline
> +struct sk_buff *rpmsg_eptdev_get_skb(struct rpmsg_eptdev *eptdev)
> +{
> + struct sk_buff *skb;
> +
> + skb = skb_dequeue(&eptdev->skb_pool);
> + if (!skb)
> + skb = alloc_skb(MAX_RPMSG_BUF_SIZE, GFP_ATOMIC);
> + return skb;
> +}
> +
> +static inline
> +void rpmsg_eptdev_put_skb(struct rpmsg_eptdev *eptdev, struct sk_buff *skb)
> +{
> + /* Recycle the skb */
> + skb->tail = 0;
> + skb->len = 0;
> + skb_queue_head(&eptdev->skb_pool, skb);
> +}
> +
> +static void rpmsg_eptdev_free_all_skb(struct rpmsg_eptdev *eptdev)
> +{
> + skb_queue_purge(&eptdev->queue);
> + skb_queue_purge(&eptdev->skb_pool);
> +}
> +
> int rpmsg_chrdev_eptdev_destroy(struct device *dev, void *data)
> {
> struct rpmsg_eptdev *eptdev = dev_to_eptdev(dev);
> @@ -99,7 +126,7 @@ static int rpmsg_ept_cb(struct rpmsg_device *rpdev, void *buf, int len,
> struct rpmsg_eptdev *eptdev = priv;
> struct sk_buff *skb;
>
> - skb = alloc_skb(len, GFP_ATOMIC);
> + skb = rpmsg_eptdev_get_skb(eptdev);
> if (!skb)
> return -ENOMEM;
>
> @@ -121,6 +148,18 @@ static int rpmsg_eptdev_open(struct inode *inode, struct file *filp)
> struct rpmsg_endpoint *ept;
> struct rpmsg_device *rpdev = eptdev->rpdev;
> struct device *dev = &eptdev->dev;
> + struct sk_buff *skb;
> + int i;
> +
> + /* Preallocate 8 SKBs */
> + for (i = 0; i < 8; i++) {
> + skb = rpmsg_eptdev_get_skb(eptdev);
> + if (!skb) {
> + rpmsg_eptdev_free_all_skb(eptdev);
> + return -ENOMEM;
> + }
> + rpmsg_eptdev_put_skb(eptdev, skb);
> + }
>
> mutex_lock(&eptdev->ept_lock);
> if (eptdev->ept) {
> @@ -168,7 +207,7 @@ static int rpmsg_eptdev_release(struct inode *inode, struct file *filp)
> mutex_unlock(&eptdev->ept_lock);
>
> /* Discard all SKBs */
> - skb_queue_purge(&eptdev->queue);
> + rpmsg_eptdev_free_all_skb(eptdev);
>
> put_device(dev);
>
> @@ -217,7 +256,7 @@ static ssize_t rpmsg_eptdev_read_iter(struct kiocb *iocb, struct iov_iter *to)
> if (copy_to_iter(skb->data, use, to) != use)
> use = -EFAULT;
>
> - kfree_skb(skb);
> + rpmsg_eptdev_put_skb(eptdev, skb);
>
> return use;
> }
> @@ -370,6 +409,7 @@ static struct rpmsg_eptdev *rpmsg_chrdev_eptdev_alloc(struct rpmsg_device *rpdev
> mutex_init(&eptdev->ept_lock);
> spin_lock_init(&eptdev->queue_lock);
> skb_queue_head_init(&eptdev->queue);
> + skb_queue_head_init(&eptdev->skb_pool);
> init_waitqueue_head(&eptdev->readq);
>
> device_initialize(dev);
> diff --git a/drivers/rpmsg/rpmsg_internal.h b/drivers/rpmsg/rpmsg_internal.h
> index 39b646d0d40d..b30bfe01db69 100644
> --- a/drivers/rpmsg/rpmsg_internal.h
> +++ b/drivers/rpmsg/rpmsg_internal.h
> @@ -15,6 +15,27 @@
> #include <linux/rpmsg.h>
> #include <linux/poll.h>
>
> +/*
> + * We're allocating buffers of 512 bytes each for communications. The
> + * number of buffers will be computed from the number of buffers supported
> + * by the vring, upto a maximum of 512 buffers (256 in each direction).
> + *
> + * Each buffer will have 16 bytes for the msg header and 496 bytes for
> + * the payload.
> + *
> + * This will utilize a maximum total space of 256KB for the buffers.
> + *
> + * We might also want to add support for user-provided buffers in time.
> + * This will allow bigger buffer size flexibility, and can also be used
> + * to achieve zero-copy messaging.
> + *
> + * Note that these numbers are purely a decision of this driver - we
> + * can change this without changing anything in the firmware of the remote
> + * processor.
> + */
> +#define MAX_RPMSG_NUM_BUFS (512)
> +#define MAX_RPMSG_BUF_SIZE (512)
This is a limitation of the virtio rpmsg implementation, there has
been efforts to make this dynamic and/or configurable. So I don't think
it's suitable to lift this limitation out of the virtio rpmsg
implementation.
Regards,
Bjorn
> +
> #define to_rpmsg_device(d) container_of(d, struct rpmsg_device, dev)
> #define to_rpmsg_driver(d) container_of(d, struct rpmsg_driver, drv)
>
> diff --git a/drivers/rpmsg/virtio_rpmsg_bus.c b/drivers/rpmsg/virtio_rpmsg_bus.c
> index 905ac7910c98..5369669d3327 100644
> --- a/drivers/rpmsg/virtio_rpmsg_bus.c
> +++ b/drivers/rpmsg/virtio_rpmsg_bus.c
> @@ -109,27 +109,6 @@ struct virtio_rpmsg_channel {
> #define to_virtio_rpmsg_channel(_rpdev) \
> container_of(_rpdev, struct virtio_rpmsg_channel, rpdev)
>
> -/*
> - * We're allocating buffers of 512 bytes each for communications. The
> - * number of buffers will be computed from the number of buffers supported
> - * by the vring, upto a maximum of 512 buffers (256 in each direction).
> - *
> - * Each buffer will have 16 bytes for the msg header and 496 bytes for
> - * the payload.
> - *
> - * This will utilize a maximum total space of 256KB for the buffers.
> - *
> - * We might also want to add support for user-provided buffers in time.
> - * This will allow bigger buffer size flexibility, and can also be used
> - * to achieve zero-copy messaging.
> - *
> - * Note that these numbers are purely a decision of this driver - we
> - * can change this without changing anything in the firmware of the remote
> - * processor.
> - */
> -#define MAX_RPMSG_NUM_BUFS (512)
> -#define MAX_RPMSG_BUF_SIZE (512)
> -
> /*
> * Local addresses are dynamically allocated on-demand.
> * We do not dynamically assign addresses from the low 1024 range,
> --
> 2.38.1
>
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