Mahmoud Mandour <ma.mando...@gmail.com> writes:
> Multicore L1 cache modelling is introduced and is supported for both
> full system emulation and linux-user.
>
> For full-system emulation, L1 icache and dcache are maintained for each
> available core, since this information is exposed to the plugin through
> `qemu_plugin_n_vcpus()`.
>
> For linux-user, a static number of cores is assumed (default 1 core, and
> can be provided as a plugin argument `cores=N`). Every memory access
> goes through one of these caches, this approach is taken as it's
> somewhat akin to what happens on real setup, where a program that
> dispatches more threads than the available cores, they'll thrash
> each other
>
> Signed-off-by: Mahmoud Mandour <ma.mando...@gmail.com>
> ---
> contrib/plugins/cache.c | 156 ++++++++++++++++++++++++++++++----------
> 1 file changed, 117 insertions(+), 39 deletions(-)
>
> diff --git a/contrib/plugins/cache.c b/contrib/plugins/cache.c
> index a452aba01c..60f7be208b 100644
> --- a/contrib/plugins/cache.c
> +++ b/contrib/plugins/cache.c
> @@ -23,11 +23,6 @@ static GRand *rng;
> static int limit;
> static bool sys;
>
> -static uint64_t dmem_accesses;
> -static uint64_t dmisses;
> -
> -static uint64_t imem_accesses;
> -static uint64_t imisses;
>
> enum EvictionPolicy {
> LRU,
> @@ -90,13 +85,22 @@ typedef struct {
> uint64_t imisses;
> } InsnData;
>
> +typedef struct {
> + uint64_t dmem_accesses;
> + uint64_t dmisses;
> + uint64_t imem_accesses;
> + uint64_t imisses;
> +} CoreStats;
> +
> void (*update_hit)(Cache *cache, int set, int blk);
> void (*update_miss)(Cache *cache, int set, int blk);
>
> void (*metadata_init)(Cache *cache);
> void (*metadata_destroy)(Cache *cache);
>
> -Cache *dcache, *icache;
> +static int cores;
> +CoreStats *stats;
> +Cache **dcaches, **icaches;
>
> static int pow_of_two(int num)
> {
> @@ -233,10 +237,6 @@ static bool bad_cache_params(int blksize, int assoc, int
> cachesize)
>
> static Cache *cache_init(int blksize, int assoc, int cachesize)
> {
> - if (bad_cache_params(blksize, assoc, cachesize)) {
> - return NULL;
> - }
> -
> Cache *cache;
> int i;
> uint64_t blk_mask;
> @@ -263,6 +263,24 @@ static Cache *cache_init(int blksize, int assoc, int
> cachesize)
> return cache;
> }
>
> +static Cache **caches_init(int blksize, int assoc, int cachesize)
> +{
> + Cache **caches;
> + int i;
> +
> + if (bad_cache_params(blksize, assoc, cachesize)) {
> + return NULL;
> + }
> +
> + caches = g_new(Cache *, cores);
> +
> + for (i = 0; i < cores; i++) {
> + caches[i] = cache_init(blksize, assoc, cachesize);
> + }
> +
> + return caches;
> +}
> +
> static int get_invalid_block(Cache *cache, uint64_t set)
> {
> int i;
> @@ -353,6 +371,7 @@ static void vcpu_mem_access(unsigned int vcpu_index,
> qemu_plugin_meminfo_t info,
> {
> uint64_t effective_addr;
> struct qemu_plugin_hwaddr *hwaddr;
> + int cache_idx;
> InsnData *insn;
>
> hwaddr = qemu_plugin_get_hwaddr(info, vaddr);
> @@ -363,17 +382,24 @@ static void vcpu_mem_access(unsigned int vcpu_index,
> qemu_plugin_meminfo_t info,
> effective_addr = hwaddr ? qemu_plugin_hwaddr_phys_addr(hwaddr) : vaddr;
>
> g_mutex_lock(&mtx);
> - if (dcache == NULL) {
> + cache_idx = vcpu_index % cores;
> + if (dcaches[cache_idx] == NULL) {
> g_mutex_unlock(&mtx);
> return;
> }
I was hoping we could avoid this with some careful atomic/memory barrier
use given dcaches is setup on init. However it's the exit case that gets
us which further increases my desire to fix the exit race in linux-user
and make sure callbacks don't occur in this case.
>
> - if (!access_cache(dcache, effective_addr)) {
> + if (!access_cache(dcaches[cache_idx], effective_addr)) {
> insn = (InsnData *) userdata;
> insn->dmisses++;
> - dmisses++;
> + if (cores > 1) {
> + stats[cores].dmisses++;
> + }
> + stats[cache_idx].dmisses++;
> + }
> + if (cores > 1) {
> + stats[cores].dmem_accesses++;
> }
> - dmem_accesses++;
> + stats[cache_idx].dmem_accesses++;
> g_mutex_unlock(&mtx);
> }
>
> @@ -381,21 +407,29 @@ static void vcpu_insn_exec(unsigned int vcpu_index,
> void *userdata)
> {
> uint64_t insn_addr;
> InsnData *insn;
> + uint64_t cache_idx;
>
> g_mutex_lock(&mtx);
> insn_addr = ((InsnData *) userdata)->addr;
>
> - if (icache == NULL) {
> + cache_idx = vcpu_index % cores;
> + if (icaches[cache_idx] == NULL) {
> g_mutex_unlock(&mtx);
> return;
> }
>
> - if (!access_cache(icache, insn_addr)) {
> + if (!access_cache(icaches[cache_idx], insn_addr)) {
> insn = (InsnData *) userdata;
> insn->imisses++;
> - imisses++;
> + if (cores > 1) {
> + stats[cores].imisses++;
> + }
> + stats[cache_idx].imisses++;
> }
> - imem_accesses++;
> + if (cores > 1) {
> + stats[cores].imem_accesses++;
> + }
I'd much rather avoid summing the stats during execution than at the end
when we can add things simply.
> + stats[cache_idx].imem_accesses++;
> g_mutex_unlock(&mtx);
> }
>
> @@ -475,6 +509,22 @@ static void cache_free(Cache *cache)
> g_free(cache);
> }
>
> +/*
> + * caches_free(): free an array of Cache structs.
> + * @caches: caches to free
> + *
> + * Calling cache_free for each cache in @caches, and then NULL-ify them so
> that
> + * we mark them as freed, other async callbacks can check to see whether a
> cache
> + * is freed already or not by checking against NULL.
> + */
> +static void caches_free(Cache **caches)
> +{
> + for (int i = 0; i < cores; i++) {
> + cache_free(caches[i]);
> + caches[i] = NULL;
> + }
> +}
> +
> static int dcmp(gconstpointer a, gconstpointer b)
> {
> InsnData *insn_a = (InsnData *) a;
> @@ -493,19 +543,38 @@ static int icmp(gconstpointer a, gconstpointer b)
>
> static void log_stats()
> {
> - g_autoptr(GString) rep = g_string_new("");
> - g_string_append_printf(rep,
> - "Data accesses: %lu, Misses: %lu\nMiss rate: %lf%%\n\n",
> - dmem_accesses,
> - dmisses,
> - ((double) dmisses / (double) dmem_accesses) * 100.0);
> -
> - g_string_append_printf(rep,
> - "Instruction accesses: %lu, Misses: %lu\nMiss rate: %lf%%\n\n",
> - imem_accesses,
> - imisses,
> - ((double) imisses / (double) imem_accesses) * 100.0);
> + int i, iters;
> + CoreStats cs;
> + double dmiss_rate, imiss_rate;
> +
> + g_autoptr(GString) rep = g_string_new("core #, data accesses, data
> misses,"
> + " dmiss rate, insn accesses,"
> + " insn misses, imiss rate\n");
> +
> + /* Only iterate and print a sum row if cores > 1 */
> + iters = cores == 1 ? 1 : cores + 1;
> + for (i = 0; i < iters; i++) {
> + cs = stats[i];
> + dmiss_rate = ((double) cs.dmisses) / (cs.dmem_accesses) * 100.0;
> + imiss_rate = ((double) cs.imisses) / (cs.imem_accesses) * 100.0;
> +
> + if (i == cores) {
> + g_string_append_printf(rep, "%-8s", "sum");
> + } else {
> + g_string_append_printf(rep, "%-8d", i);
> + }
> +
> + g_string_append_printf(rep, "%-14lu %-12lu %9.4lf%% %-14lu %-12lu"
> + " %9.4lf%%\n",
> + cs.dmem_accesses,
> + cs.dmisses,
> + cs.dmem_accesses ? dmiss_rate : 0.0,
> + cs.imem_accesses,
> + cs.imisses,
> + cs.imem_accesses ? imiss_rate : 0.0);
> + }
>
> + g_string_append(rep, "\n");
> qemu_plugin_outs(rep->str);
> }
>
> @@ -553,15 +622,14 @@ static void plugin_exit(qemu_plugin_id_t id, void *p)
> log_stats();
> log_top_insns();
>
> - cache_free(dcache);
> - dcache = NULL;
> -
> - cache_free(icache);
> - icache = NULL;
> + caches_free(dcaches);
> + caches_free(icaches);
>
> g_hash_table_destroy(miss_ht);
> miss_ht = NULL;
>
> + g_free(stats);
> +
> g_mutex_unlock(&mtx);
> }
>
> @@ -608,6 +676,8 @@ int qemu_plugin_install(qemu_plugin_id_t id, const
> qemu_info_t *info,
>
> policy = LRU;
>
> + cores = sys ? qemu_plugin_n_vcpus() : 1;
> +
> for (i = 0; i < argc; i++) {
> char *opt = argv[i];
> if (g_str_has_prefix(opt, "iblksize=")) {
> @@ -624,6 +694,8 @@ int qemu_plugin_install(qemu_plugin_id_t id, const
> qemu_info_t *info,
> dcachesize = g_ascii_strtoll(opt + 11, NULL, 10);
> } else if (g_str_has_prefix(opt, "limit=")) {
> limit = g_ascii_strtoll(opt + 6, NULL, 10);
> + } else if (g_str_has_prefix(opt, "cores=")) {
> + cores = g_ascii_strtoll(opt + 6, NULL, 10);
> } else if (g_str_has_prefix(opt, "evict=")) {
> gchar *p = opt + 6;
> if (g_strcmp0(p, "rand") == 0) {
> @@ -644,22 +716,28 @@ int qemu_plugin_install(qemu_plugin_id_t id, const
> qemu_info_t *info,
>
> policy_init();
>
> - dcache = cache_init(dblksize, dassoc, dcachesize);
> - if (!dcache) {
> + dcaches = caches_init(dblksize, dassoc, dcachesize);
> + if (!dcaches) {
> const char *err = cache_config_error(dblksize, dassoc, dcachesize);
> fprintf(stderr, "dcache cannot be constructed from given
> parameters\n");
> fprintf(stderr, "%s\n", err);
> return -1;
> }
>
> - icache = cache_init(iblksize, iassoc, icachesize);
> - if (!icache) {
> + icaches = caches_init(iblksize, iassoc, icachesize);
> + if (!icaches) {
> const char *err = cache_config_error(iblksize, iassoc, icachesize);
> fprintf(stderr, "icache cannot be constructed from given
> parameters\n");
> fprintf(stderr, "%s\n", err);
> return -1;
> }
>
> + /*
> + * plus one to save the sum in. If only one core is used then no need to
> + * get an auxiliary struct.
> + */
> + stats = g_new0(CoreStats, cores == 1 ? 1 : cores + 1);
> +
See above, lets keep the sum as a post processing step.
> qemu_plugin_register_vcpu_tb_trans_cb(id, vcpu_tb_trans);
> qemu_plugin_register_atexit_cb(id, plugin_exit, NULL);
--
Alex Bennée
