On Thu, 2011-06-02 at 21:01 +0100, Prasad Joshi wrote:
> QCOW uses two tables level1 (L1) table and level2 (L2) table. The L1 table
> points to offset of L2 table. When a QCOW image is probed, the L1 table is
> cached in the memory to avoid reading it from disk on every access. This
> caching improves the performance.
>
> The similar performance improvement can be observed when L2 tables are cached.
> It is impossible to cache all of the L2 tables because of the memory
> constraint. The patch adds L2 table caching capability for up to 128 L2
> tables,
> it uses combination of RB tree and List to manage the L2 cached tables. The
> link list implementation helps in building simple LRU structure and RB tree
> helps to search cached table efficiently
>
> The performance numbers are below, the machine was started with following
> command line arguments
>
> $ ./kvm run -d /home/prasad/VMDisks/Ubuntu10.10_64_cilk_qemu.qcow \
> > --params "root=/dev/vda1" -m 1024
>
> Without QCOW caching
> ====================
> $ bonnie++ -d tmp/ -c 10 -s 2048
> Writing a byte at a time...done
> Writing intelligently...done
> Rewriting...done
> Reading a byte at a time...done
> Reading intelligently...done
> start 'em...done...done...done...done...done...
> Create files in sequential order...done.
> Stat files in sequential order...done.
> Delete files in sequential order...done.
> Create files in random order...done.
> Stat files in random order...done.
> Delete files in random order...done.
> Version 1.96 ------Sequential Output------ --Sequential Input-
> --Random-
> Concurrency 10 -Per Chr- --Block-- -Rewrite- -Per Chr- --Block--
> --Seeks--
> Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec
> %CP
> prasad-virtual-m 2G 1043 99 555406 74 227605 55 5360 99 489080 68
> +++++ +++
> Latency 24646us 48544us 57893us 6686us 3595us 21026us
> Version 1.96 ------Sequential Create------ --------Random
> Create--------
> prasad-virtual-mach -Create-- --Read--- -Delete-- -Create-- --Read---
> -Delete--
> files /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP /sec
> %CP
> 16 +++++ +++ +++++ +++ +++++ +++ +++++ +++ +++++ +++ +++++
> +++
> Latency 343us 1175us 327us 555us 48us 82us
> 1.96,1.96,prasad-virtual-machine,10,1307043085,2G,,1043,99,555406,74,227605,55,
> 5360,99,489080,68,+++++,+++,16,,,,,+++++,+++,+++++,+++,+++++,+++,+++++,+++,
> +++++,+++,+++++,+++,24646us,48544us,57893us,6686us,3595us,21026us,343us,1175us,
> 327us,555us,48us,82us
>
> With QCOW caching
> =================
> $ bonnie++ -d tmp/ -c 10 -s 2048
> Writing a byte at a time...done
> Writing intelligently...done
> Rewriting...done
> Reading a byte at a time...done
> Reading intelligently...done
> start 'em...done...done...done...done...done...
> Create files in sequential order...done.
> Stat files in sequential order...done.
> Delete files in sequential order...done.
> Create files in random order...done.
> Stat files in random order...done.
> Delete files in random order...done.
> Version 1.96 ------Sequential Output------ --Sequential Input-
> --Random-
> Concurrency 10 -Per Chr- --Block-- -Rewrite- -Per Chr- --Block--
> --Seeks--
> Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec
> %CP
> prasad-virtual-m 2G 1033 99 467899 64 182387 41 5422 100 338294 48
> +++++ +++
> Latency 21549us 60585us 65723us 6331us 30014us 19994us
> Version 1.96 ------Sequential Create------ --------Random
> Create--------
> prasad-virtual-mach -Create-- --Read--- -Delete-- -Create-- --Read---
> -Delete--
> files /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP /sec
> %CP
> 16 +++++ +++ +++++ +++ +++++ +++ +++++ +++ +++++ +++ +++++
> +++
> Latency 478us 1142us 344us 402us 72us 98us
> 1.96,1.96,prasad-virtual-machine,10,1307042839,2G,,1033,99,467899,64,182387,41,
> 5422,100,338294,48,+++++,+++,16,,,,,+++++,+++,+++++,+++,+++++,+++,+++++,+++,
> +++++,+++,+++++,+++,21549us,60585us,65723us,6331us,30014us,19994us,478us,1142us,
> 344us,402us,72us,98us
>
> Summary of performance numbers
> ==============================
> There is not much difference with sequential character operations are
> performed, the code with caching performed better by small margin. The caching
> code performance raised by 18% to 24% with sequential block output and by 44%
> for sequentail block input. Which is understandable as the Level2 table will
> always be cached after a write operation. Random seek operation worked slower
> with caching code.
>
> Signed-off-by: Prasad Joshi <[email protected]>
> ---
> tools/kvm/disk/qcow.c | 216
> ++++++++++++++++++++++++++++++++++++++----
> tools/kvm/include/kvm/qcow.h | 17 ++++
> 2 files changed, 216 insertions(+), 17 deletions(-)
>
> diff --git a/tools/kvm/disk/qcow.c b/tools/kvm/disk/qcow.c
> index b52b734..4fa3850 100644
> --- a/tools/kvm/disk/qcow.c
> +++ b/tools/kvm/disk/qcow.c
> @@ -16,6 +16,140 @@
> #include <linux/kernel.h>
> #include <linux/types.h>
>
> +static int insert(struct rb_root *root, struct qcow_l2_cache *new)
> +{
> + struct rb_node **link = &(root->rb_node), *parent = NULL;
> + u64 offset = new->offset;
> +
> + /* search the tree */
> + while (*link) {
> + struct qcow_l2_cache *t;
> +
> + t = rb_entry(*link, struct qcow_l2_cache, node);
> + if (!t)
> + goto error;
> +
> + parent = *link;
> +
> + if (t->offset > offset)
> + link = &(*link)->rb_left;
> + else if (t->offset < offset)
> + link = &(*link)->rb_right;
> + else
> + goto out;
> + }
> +
> + /* add new node */
> + rb_link_node(&new->node, parent, link);
> + rb_insert_color(&new->node, root);
> +out:
> + return 0;
> +error:
> + return -1;
> +}
> +
> +static struct qcow_l2_cache *search(struct rb_root *root, u64 offset)
> +{
> + struct rb_node *link = root->rb_node;
> +
> + while (link) {
> + struct qcow_l2_cache *t;
> +
> + t = rb_entry(link, struct qcow_l2_cache, node);
> + if (!t)
> + goto out;
> +
> + if (t->offset > offset)
> + link = link->rb_left;
> + else if (t->offset < offset)
> + link = link->rb_right;
> + else
> + return t;
> + }
> +out:
> + return NULL;
> +}
> +
> +static void free_cache(struct qcow *q)
> +{
> + struct list_head *pos, *n;
> + struct qcow_l2_cache *t;
> + struct rb_root *r = &q->root;
> +
> + list_for_each_safe(pos, n, &q->lru_list) {
> + /* Remove cache table from the list and RB tree */
> + list_del(pos);
> + t = list_entry(pos, struct qcow_l2_cache, list);
> + rb_erase(&t->node, r);
> +
> + /* Free the cached node */
> + free(t->table);
> + free(t);
> + }
> +}
> +
> +static int cache_table(struct qcow *q, u64 *table, u64 offset)
> +{
> + struct qcow_l2_cache *n;
> + struct rb_root *r = &q->root;
> + struct qcow_l2_cache *lru;
> +
> + n = calloc(1, sizeof(struct qcow_l2_cache));
sizeof(*n)
sizeof() should use the variable name itself, not the data type. Check
out chapter 14 in 'Documentation/CodingStyle'.
> + if (!n)
> + goto error;
> +
> + n->offset = offset;
> + n->table = table;
> + n->qcow = q;
> + RB_CLEAR_NODE(&n->node);
> + INIT_LIST_HEAD(&n->list);
> +
> + if (q->no_cached == MAX_CACHE_NODES) {
> + /* Find the node for LRU replacement */
> + lru = list_first_entry(&q->lru_list, struct qcow_l2_cache,
> list);
> +
> + /* Remove the node from the cache */
> + rb_erase(&lru->node, r);
> + list_del_init(&lru->list);
> + q->no_cached--;
> +
> + /* Free the LRUed node */
> + free(lru->table);
> + free(lru);
> + }
> +
> + /* Add new node in RB Tree: Helps in searching faster */
> + if (insert(r, n) < 0)
> + goto error;
> +
> + /* Add in LRU replacement list */
> + list_add_tail(&n->list, &q->lru_list);
> + q->no_cached++;
> +
> + return 0;
> +error:
> + free(n);
> + return -1;
> +}
> +
> +static int search_table(struct qcow *q, u64 **table, u64 offset)
> +{
> + struct qcow_l2_cache *c;
> +
> + *table = NULL;
> +
> + c = search(&q->root, offset);
> + if (!c)
> + return -1;
> +
> + /* Update the LRU state */
> + list_del_init(&c->list);
> + list_add_tail(&c->list, &q->lru_list);
> +
> + *table = c->table;
> + return 0;
> +}
> +
> static inline u64 get_l1_index(struct qcow *q, u64 offset)
> {
> struct qcow_header *header = q->header;
> @@ -37,6 +171,43 @@ static inline u64 get_cluster_offset(struct qcow *q, u64
> offset)
> return offset & ((1 << header->cluster_bits)-1);
> }
>
> +static int qcow_read_l2_table(struct qcow *q, u64 **table, u64 offset)
> +{
> + struct qcow_header *header = q->header;
> + u64 size;
> + u64 i;
> + u64 *t;
> +
> + *table = NULL;
> + size = 1 << header->l2_bits;
> +
> + /* search an entry for offset in cache */
> + if (search_table(q, table, offset) >= 0)
> + return 0;
> +
> + t = calloc(size, sizeof(*t));
> + if (!t)
> + goto error;
> +
> + /* table not cached: read from the disk */
> + if (pread_in_full(q->fd, t, size * sizeof(u64), offset) < 0)
> + goto error;
> +
> + /* cache the table */
> + if (cache_table(q, t, offset) < 0)
> + goto error;
> +
> + /* change cached table to CPU's byte-order */
> + for (i = 0; i < size; i++)
> + be64_to_cpus(&t[i]);
> +
> + *table = t;
> + return 0;
> +error:
> + free(t);
> + return -1;
> +}
> +
> static ssize_t qcow_read_cluster(struct qcow *q, u64 offset, void *dst, u32
> dst_len)
> {
> struct qcow_header *header = q->header;
> @@ -51,7 +222,6 @@ static ssize_t qcow_read_cluster(struct qcow *q, u64
> offset, void *dst, u32 dst_
> u64 l1_idx;
> u64 l2_idx;
>
> - l2_table = NULL;
>
> cluster_size = 1 << header->cluster_bits;
>
> @@ -72,18 +242,16 @@ static ssize_t qcow_read_cluster(struct qcow *q, u64
> offset, void *dst, u32 dst_
> goto zero_cluster;
>
> l2_table_size = 1 << header->l2_bits;
> - l2_table = calloc(l2_table_size, sizeof(u64));
> - if (!l2_table)
> - goto out_error;
>
> - if (pread_in_full(q->fd, l2_table, l2_table_size * sizeof(u64),
> l2_table_offset) < 0)
> + /* read and cache level 2 table */
> + if (qcow_read_l2_table(q, &l2_table, l2_table_offset) < 0)
> goto out_error;
>
> l2_idx = get_l2_index(q, offset);
> if (l2_idx >= l2_table_size)
> goto out_error;
>
> - clust_start = be64_to_cpu(l2_table[l2_idx]) & ~header->oflag_mask;
> + clust_start = l2_table[l2_idx] & ~header->oflag_mask;
> if (!clust_start)
> goto zero_cluster;
>
> @@ -91,7 +259,6 @@ static ssize_t qcow_read_cluster(struct qcow *q, u64
> offset, void *dst, u32 dst_
> goto out_error;
>
> out:
> - free(l2_table);
> return length;
>
> zero_cluster:
> @@ -221,15 +388,16 @@ static ssize_t qcow_write_cluster(struct qcow *q, u64
> offset, void *buf, u32 src
> if (len > src_len)
> len = src_len;
>
> - l2t = calloc(l2t_sz, sizeof(u64));
> - if (!l2t)
> - goto error;
> -
> l2t_off = table->l1_table[l1t_idx] & ~header->oflag_mask;
> if (l2t_off) {
> - if (pread_in_full(q->fd, l2t, l2t_sz * sizeof(u64), l2t_off) <
> 0)
> - goto free_l2;
> + /* cache level2 table */
> + if (qcow_read_l2_table(q, &l2t, l2t_off) < 0)
> + goto error;
> } else {
> + l2t = calloc(l2t_sz, sizeof(*l2t));
> + if (!l2t)
> + goto error;
> +
> /* Capture the state of the consistent QCOW image */
> f_sz = file_size(q->fd);
> if (!f_sz)
> @@ -251,6 +419,13 @@ static ssize_t qcow_write_cluster(struct qcow *q, u64
> offset, void *buf, u32 src
> goto free_l2;
> }
>
> + if (cache_table(q, l2t, l2t_off) < 0) {
> + if (ftruncate(q->fd, f_sz) < 0)
> + goto free_l2;
> +
> + goto free_l2;
> + }
> +
> /* Update the in-core entry */
> table->l1_table[l1t_idx] = l2t_off;
> }
> @@ -258,17 +433,15 @@ static ssize_t qcow_write_cluster(struct qcow *q, u64
> offset, void *buf, u32 src
> /* Capture the state of the consistent QCOW image */
> f_sz = file_size(q->fd);
> if (!f_sz)
> - goto free_l2;
> + goto error;
>
> - clust_start = be64_to_cpu(l2t[l2t_idx]) & ~header->oflag_mask;
> + clust_start = l2t[l2t_idx] & ~header->oflag_mask;
> if (!clust_start) {
> clust_start = ALIGN(f_sz, clust_sz);
> update_meta = true;
> } else
> update_meta = false;
>
> - free(l2t);
> -
> /* Write actual data */
> if (pwrite_in_full(q->fd, buf, len, clust_start + clust_off) < 0)
> goto error;
> @@ -282,9 +455,13 @@ static ssize_t qcow_write_cluster(struct qcow *q, u64
> offset, void *buf, u32 src
>
> goto error;
> }
> +
> + /* Update the cached level2 entry */
> + l2t[l2t_idx] = clust_start;
> }
>
> return len;
> +
> free_l2:
> free(l2t);
> error:
> @@ -336,6 +513,7 @@ static int qcow_disk_close(struct disk_image *disk)
>
> q = disk->priv;
>
> + free_cache(q);
> free(q->table.l1_table);
> free(q->header);
> free(q);
> @@ -428,6 +606,8 @@ static struct disk_image *qcow2_probe(int fd, bool
> readonly)
> goto error;
>
> q->fd = fd;
> + q->root = RB_ROOT;
> + INIT_LIST_HEAD(&q->lru_list);
>
> h = q->header = qcow2_read_header(fd);
> if (!h)
> @@ -525,6 +705,8 @@ static struct disk_image *qcow1_probe(int fd, bool
> readonly)
> goto error;
>
> q->fd = fd;
> + q->root = RB_ROOT;
> + INIT_LIST_HEAD(&q->lru_list);
>
> h = q->header = qcow1_read_header(fd);
> if (!h)
> diff --git a/tools/kvm/include/kvm/qcow.h b/tools/kvm/include/kvm/qcow.h
> index b6e7493..1663819 100644
> --- a/tools/kvm/include/kvm/qcow.h
> +++ b/tools/kvm/include/kvm/qcow.h
> @@ -3,6 +3,8 @@
>
> #include <linux/types.h>
> #include <stdbool.h>
> +#include <linux/rbtree.h>
> +#include <linux/list.h>
>
> #define QCOW_MAGIC (('Q' << 24) | ('F' << 16) | ('I' << 8) | 0xfb)
>
> @@ -17,6 +19,16 @@
> #define QCOW2_OFLAG_COMPRESSED (1LL << 62)
> #define QCOW2_OFLAG_MASK (QCOW2_OFLAG_COPIED|QCOW2_OFLAG_COMPRESSED)
>
> +#define MAX_CACHE_NODES 128
> +
> +struct qcow_l2_cache {
> + u64 offset;
> + u64 *table;
> + struct rb_node node;
> + struct list_head list;
> + struct qcow *qcow;
I only see 'qcow' being initialized, but isn't used anywhere. Is it
really needed?
> +};
> +
> struct qcow_table {
> u32 table_size;
> u64 *l1_table;
> @@ -26,6 +38,11 @@ struct qcow {
> void *header;
> struct qcow_table table;
> int fd;
> +
> + /* Level2 caching data structures */
> + struct rb_root root;
> + struct list_head lru_list;
> + int no_cached;
> };
>
> struct qcow_header {
--
Sasha.
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