lkml.org 
[lkml]   [2022]   [Jul]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v5 03/11] 9p/trans_virtio: introduce struct virtqueue_sg
Christian Schoenebeck wrote on Tue, Jul 12, 2022 at 04:31:16PM +0200:
> The amount of elements in a scatter/gather list is limited to
> approximately 128 elements. To allow going beyond that limit
> with subsequent patches, pave the way by turning the one-
> dimensional sg list array into a two-dimensional array, i.e:
>
> sg[128]
>
> becomes
>
> sgl[nsgl][SG_MAX_SINGLE_ALLOC]
>
> As the value of 'nsgl' is exactly (still) 1 in this commit
> and the compile-time (compiler and architecture dependent)
> value of 'SG_MAX_SINGLE_ALLOC' equals approximately the
> previous hard coded 128 elements, this commit is therefore
> more of a preparatory refactoring then actual behaviour
> change.
>
> A custom struct virtqueue_sg is defined instead of using
> shared API struct sg_table, because the latter would not
> allow to resize the table after allocation. sg_append_table
> API OTOH would not fit either, because it requires a list
> of pages beforehand upon allocation. And both APIs only
> support all-or-nothing allocation.
>
> Signed-off-by: Christian Schoenebeck <linux_oss@crudebyte.com>
> ---
>
> The question is whether that should really become 9p specifc SG list
> code, or whether it should rather be squeezed into shared SG list code
> base. Opinions by maintainers needed.

hmm from the 9p side I'd say the type is simple enough that we can just
keep it here; most people don't want to resize these lists...

How much do you care about the all-or-nothing case you described in this
commit message? From the look of it, patch 6 -- at what point did you
actually see this being useful?

> net/9p/trans_virtio.c | 193 ++++++++++++++++++++++++++++++++----------
> 1 file changed, 147 insertions(+), 46 deletions(-)
>
> diff --git a/net/9p/trans_virtio.c b/net/9p/trans_virtio.c
> index 18bdfa64b934..f63cd1b08bca 100644
> --- a/net/9p/trans_virtio.c
> +++ b/net/9p/trans_virtio.c
> @@ -36,7 +36,31 @@
> #include <linux/virtio_9p.h>
> #include "trans_common.h"
>
> -#define VIRTQUEUE_DEFAULT_NUM 128
> +/**
> + * struct virtqueue_sg - (chained) scatter gather lists for virtqueue data
> + * transmission
> + * @nsgl: amount of elements (in first dimension) of array field @sgl
> + * @sgl: two-dimensional array, i.e. sgl[nsgl][SG_MAX_SINGLE_ALLOC]
> + */
> +struct virtqueue_sg {
> + unsigned int nsgl;
> + struct scatterlist *sgl[];
> +};
> +
> +/*
> + * Default value for field nsgl in struct virtqueue_sg, which defines the
> + * initial virtio data transmission capacity when this virtio transport is
> + * probed.
> + */
> +#define VIRTQUEUE_SG_NSGL_DEFAULT 1
> +
> +/* maximum value for field nsgl in struct virtqueue_sg */
> +#define VIRTQUEUE_SG_NSGL_MAX \
> + ((PAGE_SIZE - sizeof(struct virtqueue_sg)) / \
> + sizeof(struct scatterlist *)) \
> +
> +/* last entry per sg list is used for chaining (pointer to next list) */
> +#define SG_USER_PAGES_PER_LIST (SG_MAX_SINGLE_ALLOC - 1)
>
> /* a single mutex to manage channel initialization and attachment */
> static DEFINE_MUTEX(virtio_9p_lock);
> @@ -53,8 +77,7 @@ static atomic_t vp_pinned = ATOMIC_INIT(0);
> * @ring_bufs_avail: flag to indicate there is some available in the ring buf
> * @vc_wq: wait queue for waiting for thing to be added to ring buf
> * @p9_max_pages: maximum number of pinned pages
> - * @sg: scatter gather list which is used to pack a request (protected?)
> - * @sg_n: amount of elements in sg array
> + * @vq_sg: table of scatter gather lists, which are used to pack a request
> * @chan_list: linked list of channels
> *
> * We keep all per-channel information in a structure.
> @@ -77,9 +100,7 @@ struct virtio_chan {
> * will be placing it in each channel.
> */
> unsigned long p9_max_pages;
> - /* Scatterlist: can be too big for stack. */
> - struct scatterlist *sg;
> - size_t sg_n;
> + struct virtqueue_sg *vq_sg;
> /**
> * @tag: name to identify a mount null terminated
> */
> @@ -96,6 +117,92 @@ static unsigned int rest_of_page(void *data)
> return PAGE_SIZE - offset_in_page(data);
> }
>
> +/**
> + * vq_sg_page - returns user page for given page index
> + * @vq_sg: scatter gather lists used by this transport
> + * @page: user page index across all scatter gather lists
> + */
> +static struct scatterlist *vq_sg_page(struct virtqueue_sg *vq_sg, size_t page)
> +{
> + unsigned int node = page / SG_USER_PAGES_PER_LIST;
> + unsigned int leaf = page % SG_USER_PAGES_PER_LIST;
> + BUG_ON(node >= VIRTQUEUE_SG_NSGL_MAX);

probably awnt to check with vq_sg->sg_n instead?
(we already check sg_n <= MAX on alloc)


> + return &vq_sg->sgl[node][leaf];
> +}
> +
> +/**
> + * vq_sg_npages - returns total number of individual user pages in passed
> + * scatter gather lists
> + * @vq_sg: scatter gather lists to be counted
> + */
> +static size_t vq_sg_npages(struct virtqueue_sg *vq_sg)
> +{
> + return vq_sg->nsgl * SG_USER_PAGES_PER_LIST;
> +}
> +
> +/**
> + * vq_sg_free - free all memory previously allocated for @vq_sg
> + * @vq_sg: scatter gather lists to be freed
> + */
> +static void vq_sg_free(struct virtqueue_sg *vq_sg)
> +{
> + unsigned int i;
> +
> + if (!vq_sg)
> + return;
> +
> + for (i = 0; i < vq_sg->nsgl; ++i) {
> + kfree(vq_sg->sgl[i]);
> + }
> + kfree(vq_sg);
> +}
> +
> +/**
> + * vq_sg_alloc - allocates and returns @nsgl scatter gather lists
> + * @nsgl: amount of scatter gather lists to be allocated
> + * If @nsgl is larger than one then chained lists are used if supported by
> + * architecture.
> + */
> +static struct virtqueue_sg *vq_sg_alloc(unsigned int nsgl)
> +{
> + struct virtqueue_sg *vq_sg;
> + unsigned int i;
> +
> + BUG_ON(!nsgl || nsgl > VIRTQUEUE_SG_NSGL_MAX);
> +#ifdef CONFIG_ARCH_NO_SG_CHAIN
> + if (WARN_ON_ONCE(nsgl > 1))
> + return NULL;
> +#endif
> +
> + vq_sg = kzalloc(sizeof(struct virtqueue_sg) +
> + nsgl * sizeof(struct scatterlist *),
> + GFP_KERNEL);
> +
> + if (!vq_sg)
> + return NULL;
> +
> + vq_sg->nsgl = nsgl;
> +
> + for (i = 0; i < nsgl; ++i) {
> + vq_sg->sgl[i] = kmalloc_array(
> + SG_MAX_SINGLE_ALLOC, sizeof(struct scatterlist),
> + GFP_KERNEL
> + );
> + if (!vq_sg->sgl[i]) {
> + vq_sg_free(vq_sg);
> + return NULL;
> + }
> + sg_init_table(vq_sg->sgl[i], SG_MAX_SINGLE_ALLOC);
> + if (i) {
> + /* chain the lists */
> + sg_chain(vq_sg->sgl[i - 1], SG_MAX_SINGLE_ALLOC,
> + vq_sg->sgl[i]);
> + }
> + }
> + sg_mark_end(&vq_sg->sgl[nsgl - 1][SG_MAX_SINGLE_ALLOC - 1]);
> + return vq_sg;
> +}
> +
> /**
> * p9_virtio_close - reclaim resources of a channel
> * @client: client instance
> @@ -158,9 +265,8 @@ static void req_done(struct virtqueue *vq)
>
> /**
> * pack_sg_list - pack a scatter gather list from a linear buffer
> - * @sg: scatter/gather list to pack into
> + * @vq_sg: scatter/gather lists to pack into
> * @start: which segment of the sg_list to start at
> - * @limit: maximum segment to pack data to
> * @data: data to pack into scatter/gather list
> * @count: amount of data to pack into the scatter/gather list
> *
> @@ -170,11 +276,12 @@ static void req_done(struct virtqueue *vq)
> *
> */
>
> -static int pack_sg_list(struct scatterlist *sg, int start,
> - int limit, char *data, int count)
> +static int pack_sg_list(struct virtqueue_sg *vq_sg, int start,
> + char *data, int count)
> {
> int s;
> int index = start;
> + size_t limit = vq_sg_npages(vq_sg);
>
> while (count) {
> s = rest_of_page(data);
> @@ -182,13 +289,13 @@ static int pack_sg_list(struct scatterlist *sg, int start,
> s = count;
> BUG_ON(index >= limit);
> /* Make sure we don't terminate early. */
> - sg_unmark_end(&sg[index]);
> - sg_set_buf(&sg[index++], data, s);
> + sg_unmark_end(vq_sg_page(vq_sg, index));
> + sg_set_buf(vq_sg_page(vq_sg, index++), data, s);
> count -= s;
> data += s;
> }
> if (index-start)
> - sg_mark_end(&sg[index - 1]);
> + sg_mark_end(vq_sg_page(vq_sg, index - 1));
> return index-start;
> }
>
> @@ -208,21 +315,21 @@ static int p9_virtio_cancelled(struct p9_client *client, struct p9_req_t *req)
> /**
> * pack_sg_list_p - Just like pack_sg_list. Instead of taking a buffer,
> * this takes a list of pages.
> - * @sg: scatter/gather list to pack into
> + * @vq_sg: scatter/gather lists to pack into
> * @start: which segment of the sg_list to start at
> - * @limit: maximum number of pages in sg list.
> * @pdata: a list of pages to add into sg.
> * @nr_pages: number of pages to pack into the scatter/gather list
> * @offs: amount of data in the beginning of first page _not_ to pack
> * @count: amount of data to pack into the scatter/gather list
> */
> static int
> -pack_sg_list_p(struct scatterlist *sg, int start, int limit,
> +pack_sg_list_p(struct virtqueue_sg *vq_sg, int start,
> struct page **pdata, int nr_pages, size_t offs, int count)
> {
> int i = 0, s;
> int data_off = offs;
> int index = start;
> + size_t limit = vq_sg_npages(vq_sg);
>
> BUG_ON(nr_pages > (limit - start));
> /*
> @@ -235,15 +342,16 @@ pack_sg_list_p(struct scatterlist *sg, int start, int limit,
> s = count;
> BUG_ON(index >= limit);
> /* Make sure we don't terminate early. */
> - sg_unmark_end(&sg[index]);
> - sg_set_page(&sg[index++], pdata[i++], s, data_off);
> + sg_unmark_end(vq_sg_page(vq_sg, index));
> + sg_set_page(vq_sg_page(vq_sg, index++), pdata[i++], s,
> + data_off);
> data_off = 0;
> count -= s;
> nr_pages--;
> }
>
> if (index-start)
> - sg_mark_end(&sg[index - 1]);
> + sg_mark_end(vq_sg_page(vq_sg, index - 1));
> return index - start;
> }
>
> @@ -271,15 +379,13 @@ p9_virtio_request(struct p9_client *client, struct p9_req_t *req)
>
> out_sgs = in_sgs = 0;
> /* Handle out VirtIO ring buffers */
> - out = pack_sg_list(chan->sg, 0,
> - chan->sg_n, req->tc.sdata, req->tc.size);
> + out = pack_sg_list(chan->vq_sg, 0, req->tc.sdata, req->tc.size);
> if (out)
> - sgs[out_sgs++] = chan->sg;
> + sgs[out_sgs++] = vq_sg_page(chan->vq_sg, 0);
>
> - in = pack_sg_list(chan->sg, out,
> - chan->sg_n, req->rc.sdata, req->rc.capacity);
> + in = pack_sg_list(chan->vq_sg, out, req->rc.sdata, req->rc.capacity);
> if (in)
> - sgs[out_sgs + in_sgs++] = chan->sg + out;
> + sgs[out_sgs + in_sgs++] = vq_sg_page(chan->vq_sg, out);
>
> err = virtqueue_add_sgs(chan->vq, sgs, out_sgs, in_sgs, req,
> GFP_ATOMIC);
> @@ -448,16 +554,15 @@ p9_virtio_zc_request(struct p9_client *client, struct p9_req_t *req,
> out_sgs = in_sgs = 0;
>
> /* out data */
> - out = pack_sg_list(chan->sg, 0,
> - chan->sg_n, req->tc.sdata, req->tc.size);
> + out = pack_sg_list(chan->vq_sg, 0, req->tc.sdata, req->tc.size);
>
> if (out)
> - sgs[out_sgs++] = chan->sg;
> + sgs[out_sgs++] = vq_sg_page(chan->vq_sg, 0);
>
> if (out_pages) {
> - sgs[out_sgs++] = chan->sg + out;
> - out += pack_sg_list_p(chan->sg, out, chan->sg_n,
> - out_pages, out_nr_pages, offs, outlen);
> + sgs[out_sgs++] = vq_sg_page(chan->vq_sg, out);
> + out += pack_sg_list_p(chan->vq_sg, out, out_pages,
> + out_nr_pages, offs, outlen);
> }
>
> /*
> @@ -467,15 +572,14 @@ p9_virtio_zc_request(struct p9_client *client, struct p9_req_t *req,
> * Arrange in such a way that server places header in the
> * allocated memory and payload onto the user buffer.
> */
> - in = pack_sg_list(chan->sg, out,
> - chan->sg_n, req->rc.sdata, in_hdr_len);
> + in = pack_sg_list(chan->vq_sg, out, req->rc.sdata, in_hdr_len);
> if (in)
> - sgs[out_sgs + in_sgs++] = chan->sg + out;
> + sgs[out_sgs + in_sgs++] = vq_sg_page(chan->vq_sg, out);
>
> if (in_pages) {
> - sgs[out_sgs + in_sgs++] = chan->sg + out + in;
> - in += pack_sg_list_p(chan->sg, out + in, chan->sg_n,
> - in_pages, in_nr_pages, offs, inlen);
> + sgs[out_sgs + in_sgs++] = vq_sg_page(chan->vq_sg, out + in);
> + in += pack_sg_list_p(chan->vq_sg, out + in, in_pages,
> + in_nr_pages, offs, inlen);
> }
>
> BUG_ON(out_sgs + in_sgs > ARRAY_SIZE(sgs));
> @@ -576,14 +680,12 @@ static int p9_virtio_probe(struct virtio_device *vdev)
> goto fail;
> }
>
> - chan->sg = kmalloc_array(VIRTQUEUE_DEFAULT_NUM,
> - sizeof(struct scatterlist), GFP_KERNEL);
> - if (!chan->sg) {
> + chan->vq_sg = vq_sg_alloc(VIRTQUEUE_SG_NSGL_DEFAULT);
> + if (!chan->vq_sg) {
> pr_err("Failed to allocate virtio 9P channel\n");
> err = -ENOMEM;
> goto out_free_chan_shallow;
> }
> - chan->sg_n = VIRTQUEUE_DEFAULT_NUM;
>
> chan->vdev = vdev;
>
> @@ -596,8 +698,6 @@ static int p9_virtio_probe(struct virtio_device *vdev)
> chan->vq->vdev->priv = chan;
> spin_lock_init(&chan->lock);
>
> - sg_init_table(chan->sg, chan->sg_n);
> -
> chan->inuse = false;
> if (virtio_has_feature(vdev, VIRTIO_9P_MOUNT_TAG)) {
> virtio_cread(vdev, struct virtio_9p_config, tag_len, &tag_len);
> @@ -646,7 +746,7 @@ static int p9_virtio_probe(struct virtio_device *vdev)
> out_free_vq:
> vdev->config->del_vqs(vdev);
> out_free_chan:
> - kfree(chan->sg);
> + vq_sg_free(chan->vq_sg);
> out_free_chan_shallow:
> kfree(chan);
> fail:
> @@ -741,7 +841,7 @@ static void p9_virtio_remove(struct virtio_device *vdev)
> kobject_uevent(&(vdev->dev.kobj), KOBJ_CHANGE);
> kfree(chan->tag);
> kfree(chan->vc_wq);
> - kfree(chan->sg);
> + vq_sg_free(chan->vq_sg);
> kfree(chan);
>
> }
> @@ -780,7 +880,8 @@ static struct p9_trans_module p9_virtio_trans = {
> * that are not at page boundary, that can result in an extra
> * page in zero copy.
> */
> - .maxsize = PAGE_SIZE * (VIRTQUEUE_DEFAULT_NUM - 3),
> + .maxsize = PAGE_SIZE *
> + ((VIRTQUEUE_SG_NSGL_DEFAULT * SG_USER_PAGES_PER_LIST) - 3),
> .def = 1,
> .owner = THIS_MODULE,
> };

\
 
 \ /
  Last update: 2022-07-12 22:35    [W:0.170 / U:0.024 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site