Re: [Qemu-devel] [PATCH v9 01/10] Add cache handling functions

[Anthony Liguori]

On 04/11/2012 01:49 PM, Orit Wasserman wrote:
> Add LRU page cache mechanism.
> The page are accessed by their address.
>
> Signed-off-by: Orit Wasserman<address@hidden>
> Signed-off-by: Benoit Hudzia<address@hidden>
> Signed-off-by: Petter Svard<address@hidden>
> Signed-off-by: Aidan Shribman<address@hidden>
> ---
>   arch_init.c |  220 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>   1 files changed, 220 insertions(+), 0 deletions(-)
>
> diff --git a/arch_init.c b/arch_init.c
> index 595badf..2e534f1 100644
> --- a/arch_init.c
> +++ b/arch_init.c
> @@ -28,6 +28,7 @@
>   #include<sys/types.h>
>   #include<sys/mman.h>
>   #endif
> +#include<assert.h>
>   #include "config.h"
>   #include "monitor.h"
>   #include "sysemu.h"
> @@ -44,6 +45,14 @@
>   #include "exec-memory.h"
>   #include "hw/pcspk.h"
>
> +#ifdef DEBUG_ARCH_INIT
> +#define DPRINTF(fmt, ...) \
> +    do { fprintf(stdout, "arch_init: " fmt, ## __VA_ARGS__); } while (0)
> +#else
> +#define DPRINTF(fmt, ...) \
> +    do { } while (0)
> +#endif
> +
>   #ifdef TARGET_SPARC
>   int graphic_width = 1024;
>   int graphic_height = 768;
> @@ -127,6 +136,217 @@ static int is_dup_page(uint8_t *page)
>       return 1;
>   }
>
> +/***********************************************************/
> +/* Page cache for storing previous pages as basis for XBZRLE compression */
> +#define CACHE_N_WAY 2 /* 2-way assossiative cache */
> +
> +typedef struct CacheItem {
> +    ram_addr_t it_addr;
> +    unsigned long it_age;
> +    uint8_t *it_data;
> +} CacheItem;
> +
> +typedef struct CacheBucket {
> +    CacheItem bkt_item[CACHE_N_WAY];
> +} CacheBucket;
> +
> +static CacheBucket *page_cache;
> +static int64_t cache_num_buckets;
> +static uint64_t cache_max_item_age;
> +static int64_t cache_num_items;
> +
> +static void cache_init(int64_t num_buckets);
> +static void cache_fini(void);
> +static int cache_is_cached(ram_addr_t addr);
> +static int cache_get_oldest(CacheBucket *buck);
> +static int cache_get_newest(CacheBucket *buck, ram_addr_t addr);
> +static void cache_insert(ram_addr_t id, uint8_t *pdata, int use_buffer);
> +static unsigned long cache_get_cache_pos(ram_addr_t address);
> +static CacheItem *cache_item_get(unsigned long pos, int item);
> +static void cache_resize(int64_t new_size);
> +
> +/***********************************************************/
> +/* XBRLE page cache implementation */
> +static CacheItem *cache_item_get(unsigned long pos, int item)
> +{
> +    assert(page_cache);
> +    return&page_cache[pos].bkt_item[item];
> +}
> +
> +static void cache_init(int64_t num_bytes)

If we're caching pages, let's take a num_pages argument.  Then we can avoid 
TARGET_PAGE_SIZE and move this to it's own cache.c file and build it once.

Let's also make a proper header (include/qemu/cache.h) and document the public 
functions.  I really am not convinced we need a custom data structure here but 
if we're going to add one, we should make at least a small attempt to make it 
reusable.

> +{
> +    int i;
> +
> +    cache_num_items = 0;
> +    cache_max_item_age = 0;
> +    cache_num_buckets = num_bytes / (TARGET_PAGE_SIZE * CACHE_N_WAY);
> +    assert(cache_num_buckets);

use g_assert instead and drop the explicit include of assert.h

> +    DPRINTF("Setting cache buckets to %lu\n", cache_num_buckets);
> +
> +    assert(!page_cache);

return page_cache instead of using a global

> +    page_cache = (CacheBucket *)g_malloc((cache_num_buckets) *
> +            sizeof(CacheBucket));
> +
> +    for (i = 0; i<  cache_num_buckets; i++) {
> +        int j;
> +        for (j = 0; j<  CACHE_N_WAY; j++) {
> +            CacheItem *it = cache_item_get(i, j);
> +            it->it_data = NULL;
> +            it->it_age = 0;
> +            it->it_addr = -1;
> +        }
> +    }
> +}
> +
> +static void cache_fini(void)
> +{
> +    int i;


Take page_cache as an argument here.

> +    assert(page_cache);
> +
> +    for (i = 0; i<  cache_num_buckets; i++) {
> +        int j;
> +        for (j = 0; j<  CACHE_N_WAY; j++) {
> +            CacheItem *it = cache_item_get(i, j);
> +            g_free(it->it_data);
> +            it->it_data = 0;
> +        }
> +    }
> +
> +    g_free(page_cache);
> +    page_cache = NULL;
> +}
> +
> +static unsigned long cache_get_cache_pos(ram_addr_t address)
> +{
> +    unsigned long pos;
> +
> +    assert(cache_num_buckets);

And here, etc.

> +    pos = (address/TARGET_PAGE_SIZE)&  (cache_num_buckets - 1);
> +    return pos;
> +}
> +
> +static int cache_get_newest(CacheBucket *buck, ram_addr_t addr)
> +{
> +    unsigned long big = 0;
> +    int big_pos = -1;
> +    int j;
> +
> +    assert(page_cache);
> +
> +    for (j = 0; j<  CACHE_N_WAY; j++) {
> +        CacheItem *it =&buck->bkt_item[j];
> +
> +        if (it->it_addr != addr) {
> +            continue;
> +        }
> +
> +        if (!j || it->it_age>  big) {
> +            big = it->it_age;
> +            big_pos = j;
> +        }
> +    }
> +
> +    return big_pos;
> +}
> +
> +static int cache_get_oldest(CacheBucket *buck)
> +{
> +    unsigned long small = 0;
> +    int small_pos = -1;
> +    int j;
> +
> +    assert(page_cache);
> +
> +    for (j = 0; j<  CACHE_N_WAY; j++) {
> +        CacheItem *it =&buck->bkt_item[j];
> +
> +        if (!j || it->it_age<   small) {
> +            small = it->it_age;
> +            small_pos = j;
> +        }
> +    }
> +
> +    return small_pos;
> +}
> +
> +static int cache_is_cached(ram_addr_t addr)
> +{
> +    unsigned long pos = cache_get_cache_pos(addr);
> +
> +    assert(page_cache);
> +    CacheBucket *bucket =&page_cache[pos];
> +    return cache_get_newest(bucket, addr);
> +}
> +
> +static void cache_insert(unsigned long addr, uint8_t *pdata, int use_buffer)
> +{
> +    unsigned long pos;
> +    int slot = -1;
> +    CacheBucket *bucket;
> +
> +    pos = cache_get_cache_pos(addr);
> +    assert(page_cache);
> +    bucket =&page_cache[pos];
> +    slot = cache_get_oldest(bucket); /* evict LRU */
> +
> +    /* actual update of entry */
> +    CacheItem *it = cache_item_get(pos, slot);

This is done a lot.  We don't use C99 declarations in QEMU.  Please move all the 
variable declarations to the top of the functions.

Regards,

Anthony Liguori


> +    if (!it->it_data) {
> +        if (!use_buffer) {
> +            it->it_data = g_malloc(TARGET_PAGE_SIZE);
> +        }
> +        cache_num_items++;
> +    }
> +
> +    if (!use_buffer) {
> +        memcpy(it->it_data, pdata, TARGET_PAGE_SIZE);
> +    } else {
> +        it->it_data = pdata;
> +    }
> +    it->it_age = ++cache_max_item_age;
> +    it->it_addr = addr;
> +}
> +
> +void cache_resize(int64_t new_size)
> +{
> +    int64_t new_num_buckets = new_size/(TARGET_PAGE_SIZE * CACHE_N_WAY);
> +    CacheBucket *old_page_cache = page_cache;
> +    int i;
> +    int64_t old_num_buckets = cache_num_buckets;
> +
> +    /* same size */
> +    if (new_num_buckets == cache_num_buckets) {
> +        return;
> +    }
> +    /* cache was not inited */
> +    if (page_cache == NULL) {
> +        return;
> +    }
> +
> +    /* create a new cache */
> +    page_cache = NULL;
> +    cache_init(new_size);
> +
> +    /* move all data from old cache */
> +    for (i = 0; i<  old_num_buckets; i++) {
> +        int j;
> +        for (j = 0; j<  CACHE_N_WAY; j++) {
> +            CacheItem *it =&old_page_cache[i].bkt_item[j];
> +            if (it->it_addr != -1) {
> +                /* check for collision , if there is keep the first value */
> +                if (cache_is_cached(it->it_addr) != -1) {
> +                    g_free(it->it_data);
> +                } else {
> +                    cache_insert(it->it_addr, it->it_data, 1);
> +                }
> +            }
> +        }
> +    }
> +
> +    g_free(old_page_cache);
> +}
> +
>   static RAMBlock *last_block;
>   static ram_addr_t last_offset;