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Re: [Qemu-devel] [PATCH RFC 3/3] xen_disk: add persistent grant support
From: |
Blue Swirl |
Subject: |
Re: [Qemu-devel] [PATCH RFC 3/3] xen_disk: add persistent grant support to xen_disk backend |
Date: |
Fri, 4 Jan 2013 21:01:43 +0000 |
On Mon, Dec 31, 2012 at 12:16 PM, Roger Pau Monne <address@hidden> wrote:
> This protocol extension reuses the same set of grant pages for all
> transactions between the front/back drivers, avoiding expensive tlb
> flushes, grant table lock contention and switches between userspace
> and kernel space. The full description of the protocol can be found in
> the public blkif.h header.
>
> Speed improvement with 15 guests performing I/O is ~450%.
>
> Signed-off-by: Roger Pau Monné <address@hidden>
> Cc: address@hidden
> Cc: Stefano Stabellini <address@hidden>
> Cc: Anthony PERARD <address@hidden>
> ---
> Performance comparison with the previous implementation can be seen in
> the followign graph:
>
> http://xenbits.xen.org/people/royger/persistent_read_qemu.png
> ---
> hw/xen_disk.c | 155 ++++++++++++++++++++++++++++++++++++++++++++++++++------
> 1 files changed, 138 insertions(+), 17 deletions(-)
>
> diff --git a/hw/xen_disk.c b/hw/xen_disk.c
> index 1eb485a..bafeceb 100644
> --- a/hw/xen_disk.c
> +++ b/hw/xen_disk.c
> @@ -52,6 +52,11 @@ static int max_requests = 32;
> #define BLOCK_SIZE 512
> #define IOCB_COUNT (BLKIF_MAX_SEGMENTS_PER_REQUEST + 2)
>
> +struct persistent_gnt {
This should be PersistentGrant and don't forget to add a typedef.
> + void *page;
> + struct XenBlkDev *blkdev;
> +};
> +
> struct ioreq {
> blkif_request_t req;
> int16_t status;
> @@ -69,6 +74,7 @@ struct ioreq {
> int prot;
> void *page[BLKIF_MAX_SEGMENTS_PER_REQUEST];
> void *pages;
> + int num_unmap;
>
> /* aio status */
> int aio_inflight;
> @@ -105,6 +111,12 @@ struct XenBlkDev {
> int requests_inflight;
> int requests_finished;
>
> + /* Persistent grants extension */
> + gboolean feature_persistent;
> + GTree *persistent_gnts;
> + unsigned int persistent_gnt_c;
> + unsigned int max_grants;
> +
> /* qemu block driver */
> DriveInfo *dinfo;
> BlockDriverState *bs;
> @@ -138,6 +150,29 @@ static void ioreq_reset(struct ioreq *ioreq)
> qemu_iovec_reset(&ioreq->v);
> }
>
> +static gint int_cmp(gconstpointer a, gconstpointer b, gpointer user_data)
> +{
> + uint ua = GPOINTER_TO_UINT(a);
> + uint ub = GPOINTER_TO_UINT(b);
> + return (ua > ub) - (ua < ub);
> +}
> +
> +static void destroy_grant(gpointer pgnt)
> +{
> + struct persistent_gnt *grant = pgnt;
> + XenGnttab gnt = grant->blkdev->xendev.gnttabdev;
> +
> + if (xc_gnttab_munmap(gnt, grant->page, 1) != 0) {
> + xen_be_printf(&grant->blkdev->xendev, 0,
> + "xc_gnttab_munmap failed: %s\n",
> + strerror(errno));
> + }
> + grant->blkdev->persistent_gnt_c--;
> + xen_be_printf(&grant->blkdev->xendev, 3,
> + "unmapped grant %p\n", grant->page);
> + g_free(grant);
> +}
> +
> static struct ioreq *ioreq_start(struct XenBlkDev *blkdev)
> {
> struct ioreq *ioreq = NULL;
> @@ -266,21 +301,21 @@ static void ioreq_unmap(struct ioreq *ioreq)
> XenGnttab gnt = ioreq->blkdev->xendev.gnttabdev;
> int i;
>
> - if (ioreq->v.niov == 0 || ioreq->mapped == 0) {
> + if (ioreq->num_unmap == 0 || ioreq->mapped == 0) {
> return;
> }
> if (batch_maps) {
> if (!ioreq->pages) {
> return;
> }
> - if (xc_gnttab_munmap(gnt, ioreq->pages, ioreq->v.niov) != 0) {
> + if (xc_gnttab_munmap(gnt, ioreq->pages, ioreq->num_unmap) != 0) {
> xen_be_printf(&ioreq->blkdev->xendev, 0, "xc_gnttab_munmap
> failed: %s\n",
> strerror(errno));
> }
> - ioreq->blkdev->cnt_map -= ioreq->v.niov;
> + ioreq->blkdev->cnt_map -= ioreq->num_unmap;
> ioreq->pages = NULL;
> } else {
> - for (i = 0; i < ioreq->v.niov; i++) {
> + for (i = 0; i < ioreq->num_unmap; i++) {
> if (!ioreq->page[i]) {
> continue;
> }
> @@ -298,41 +333,107 @@ static void ioreq_unmap(struct ioreq *ioreq)
> static int ioreq_map(struct ioreq *ioreq)
> {
> XenGnttab gnt = ioreq->blkdev->xendev.gnttabdev;
> - int i;
> + uint32_t domids[BLKIF_MAX_SEGMENTS_PER_REQUEST];
> + uint32_t refs[BLKIF_MAX_SEGMENTS_PER_REQUEST];
> + void *page[BLKIF_MAX_SEGMENTS_PER_REQUEST];
> + int i, j, new_maps = 0;
> + struct persistent_gnt *grant;
>
> if (ioreq->v.niov == 0 || ioreq->mapped == 1) {
> return 0;
> }
> - if (batch_maps) {
> + if (ioreq->blkdev->feature_persistent) {
> + for (i = 0; i < ioreq->v.niov; i++) {
> + grant = g_tree_lookup(ioreq->blkdev->persistent_gnts,
> + GUINT_TO_POINTER(ioreq->refs[i]));
> +
> + if (grant != NULL) {
> + page[i] = grant->page;
> + xen_be_printf(&ioreq->blkdev->xendev, 3,
> + "using persistent-grant %" PRIu32 "\n",
> + ioreq->refs[i]);
> + } else {
> + /* Add the grant to the list of grants that
> + * should be mapped
> + */
> + domids[new_maps] = ioreq->domids[i];
> + refs[new_maps] = ioreq->refs[i];
> + page[i] = NULL;
> + new_maps++;
> + }
> + }
> + /* Set the protection to RW, since grants may be reused later
> + * with a different protection than the one needed for this request
> + */
> + ioreq->prot = PROT_WRITE | PROT_READ;
> + } else {
> + /* All grants in the request should be mapped */
> + memcpy(refs, ioreq->refs, sizeof(refs));
> + memcpy(domids, ioreq->domids, sizeof(domids));
> + memset(page, 0, sizeof(page));
> + new_maps = ioreq->v.niov;
> + }
> +
> + if (batch_maps && new_maps) {
> ioreq->pages = xc_gnttab_map_grant_refs
> - (gnt, ioreq->v.niov, ioreq->domids, ioreq->refs, ioreq->prot);
> + (gnt, new_maps, domids, refs, ioreq->prot);
> if (ioreq->pages == NULL) {
> xen_be_printf(&ioreq->blkdev->xendev, 0,
> "can't map %d grant refs (%s, %d maps)\n",
> - ioreq->v.niov, strerror(errno),
> ioreq->blkdev->cnt_map);
> + new_maps, strerror(errno), ioreq->blkdev->cnt_map);
> return -1;
> }
> - for (i = 0; i < ioreq->v.niov; i++) {
> - ioreq->v.iov[i].iov_base = ioreq->pages + i * XC_PAGE_SIZE +
> - (uintptr_t)ioreq->v.iov[i].iov_base;
> + for (i = 0, j = 0; i < ioreq->v.niov; i++) {
> + if (page[i] == NULL)
> + page[i] = ioreq->pages + (j++) * XC_PAGE_SIZE;
> }
> - ioreq->blkdev->cnt_map += ioreq->v.niov;
> - } else {
> - for (i = 0; i < ioreq->v.niov; i++) {
> + ioreq->blkdev->cnt_map += new_maps;
> + } else if (new_maps) {
> + for (i = 0; i < new_maps; i++) {
> ioreq->page[i] = xc_gnttab_map_grant_ref
> - (gnt, ioreq->domids[i], ioreq->refs[i], ioreq->prot);
> + (gnt, domids[i], refs[i], ioreq->prot);
> if (ioreq->page[i] == NULL) {
> xen_be_printf(&ioreq->blkdev->xendev, 0,
> "can't map grant ref %d (%s, %d maps)\n",
> - ioreq->refs[i], strerror(errno),
> ioreq->blkdev->cnt_map);
> + refs[i], strerror(errno),
> ioreq->blkdev->cnt_map);
> ioreq_unmap(ioreq);
> return -1;
> }
> - ioreq->v.iov[i].iov_base = ioreq->page[i] +
> (uintptr_t)ioreq->v.iov[i].iov_base;
> ioreq->blkdev->cnt_map++;
> }
> + for (i = 0, j = 0; i < ioreq->v.niov; i++) {
> + if (page[i] == NULL)
> + page[i] = ioreq->page[j++];
> + }
> + }
> + if (ioreq->blkdev->feature_persistent) {
> + while((ioreq->blkdev->persistent_gnt_c < ioreq->blkdev->max_grants)
> &&
> + new_maps) {
> + /* Go through the list of newly mapped grants and add as many
> + * as possible to the list of persistently mapped grants
> + */
> + grant = g_malloc0(sizeof(*grant));
> + new_maps--;
> + if (batch_maps)
> + grant->page = ioreq->pages + (new_maps) * XC_PAGE_SIZE;
> + else
> + grant->page = ioreq->page[new_maps];
> + grant->blkdev = ioreq->blkdev;
> + xen_be_printf(&ioreq->blkdev->xendev, 3,
> + "adding grant %" PRIu32 " page: %p\n",
> + refs[new_maps], grant->page);
> + g_tree_insert(ioreq->blkdev->persistent_gnts,
> + GUINT_TO_POINTER(refs[new_maps]),
> + grant);
> + ioreq->blkdev->persistent_gnt_c++;
> + }
> + }
> + for (i = 0; i < ioreq->v.niov; i++) {
> + ioreq->v.iov[i].iov_base = page[i] +
> + (uintptr_t)ioreq->v.iov[i].iov_base;
> }
> ioreq->mapped = 1;
> + ioreq->num_unmap = new_maps;
> return 0;
> }
>
> @@ -690,6 +791,7 @@ static int blk_init(struct XenDevice *xendev)
>
> /* fill info */
> xenstore_write_be_int(&blkdev->xendev, "feature-barrier", 1);
> + xenstore_write_be_int(&blkdev->xendev, "feature-persistent", 1);
> xenstore_write_be_int(&blkdev->xendev, "info", info);
> xenstore_write_be_int(&blkdev->xendev, "sector-size",
> blkdev->file_blk);
> xenstore_write_be_int(&blkdev->xendev, "sectors",
> @@ -713,6 +815,7 @@ out_error:
> static int blk_connect(struct XenDevice *xendev)
> {
> struct XenBlkDev *blkdev = container_of(xendev, struct XenBlkDev,
> xendev);
> + int pers;
>
> if (xenstore_read_fe_int(&blkdev->xendev, "ring-ref", &blkdev->ring_ref)
> == -1) {
> return -1;
> @@ -721,6 +824,11 @@ static int blk_connect(struct XenDevice *xendev)
> &blkdev->xendev.remote_port) == -1) {
> return -1;
> }
> + if (xenstore_read_fe_int(&blkdev->xendev, "feature-persistent", &pers)) {
> + blkdev->feature_persistent = FALSE;
> + } else {
> + blkdev->feature_persistent = !!pers;
> + }
>
> blkdev->protocol = BLKIF_PROTOCOL_NATIVE;
> if (blkdev->xendev.protocol) {
> @@ -764,6 +872,15 @@ static int blk_connect(struct XenDevice *xendev)
> }
> }
>
> + if (blkdev->feature_persistent) {
> + /* Init persistent grants */
> + blkdev->max_grants = max_requests * BLKIF_MAX_SEGMENTS_PER_REQUEST;
> + blkdev->persistent_gnts = g_tree_new_full((GCompareDataFunc)int_cmp,
> + NULL, NULL,
> + (GDestroyNotify)destroy_grant);
> + blkdev->persistent_gnt_c = 0;
> + }
> +
> xen_be_bind_evtchn(&blkdev->xendev);
>
> xen_be_printf(&blkdev->xendev, 1, "ok: proto %s, ring-ref %d, "
> @@ -804,6 +921,10 @@ static int blk_free(struct XenDevice *xendev)
> blk_disconnect(xendev);
> }
>
> + /* Free persistent grants */
> + if (blkdev->feature_persistent)
> + g_tree_destroy(blkdev->persistent_gnts);
> +
> while (!QLIST_EMPTY(&blkdev->freelist)) {
> ioreq = QLIST_FIRST(&blkdev->freelist);
> QLIST_REMOVE(ioreq, list);
> --
> 1.7.7.5 (Apple Git-26)
>
>