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qht: do not segfault when gathering stats from an uninitialized qht

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So far, QHT functions assume that the passed qht has previously been
initialized--otherwise they segfault.

This patch makes an exception for qht_statistics_init, with the goal
of simplifying calling code. For instance, qht_statistics_init is
called from the 'info jit' dump, and given that under KVM the TB qht
is never initialized, we get a segfault. Thus, instead of complicating
the 'info jit' code with additional checks, let's allow passing an
uninitialized qht to qht_statistics_init.

While at it, add a test for this to test-qht.

Before the patch (for $ qemu -enable-kvm [...]):
(qemu) info jit
[...]
direct jump count   0 (0%) (2 jumps=0 0%)
Program received signal SIGSEGV, Segmentation fault.

After the patch the "TB hash buckets", "TB hash occupancy"
and "TB hash avg chain" lines are omitted.
(qemu) info jit
[...]
direct jump count   0 (0%) (2 jumps=0 0%)
TB hash buckets     0/0 (-nan% head buckets used)
TB hash occupancy   nan% avg chain occ. Histogram: (null)
TB hash avg chain   nan buckets. Histogram: (null)
[...]

Reported by: Changlong Xie <xiecl.fnst@cn.fujitsu.com>
Signed-off-by: Emilio G. Cota <cota@braap.org>
Message-Id: <1469205390-14369-1-git-send-email-cota@braap.org>
[Extract printing statistics to an entirely separate function. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Emilio G. Cota 2016-07-22 12:36:30 -04:00 committed by Paolo Bonzini
parent 767db021bc
commit 7266ae91a1
3 changed files with 49 additions and 32 deletions
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4
tests/test-qht.c
View File

@ -95,8 +95,12 @@ static void iter_check(unsigned int count)
static void qht_do_test(unsigned int mode, size_t init_entries)
{
/* under KVM we might fetch stats from an uninitialized qht */
check_n(0);
qht_init(&ht, 0, mode);
check_n(0);
insert(0, N);
check(0, N, true);
check_n(N);

70
translate-all.c
View File

@ -1663,15 +1663,50 @@ void tb_flush_jmp_cache(CPUState *cpu, target_ulong addr)
TB_JMP_PAGE_SIZE * sizeof(TranslationBlock *));
}
static void print_qht_statistics(FILE *f, fprintf_function cpu_fprintf,
struct qht_stats hst)
{
uint32_t hgram_opts;
size_t hgram_bins;
char *hgram;
if (!hst.head_buckets) {
return;
}
cpu_fprintf(f, "TB hash buckets %zu/%zu (%0.2f%% head buckets used)\n",
hst.used_head_buckets, hst.head_buckets,
(double)hst.used_head_buckets / hst.head_buckets * 100);
hgram_opts = QDIST_PR_BORDER | QDIST_PR_LABELS;
hgram_opts |= QDIST_PR_100X | QDIST_PR_PERCENT;
if (qdist_xmax(&hst.occupancy) - qdist_xmin(&hst.occupancy) == 1) {
hgram_opts |= QDIST_PR_NODECIMAL;
}
hgram = qdist_pr(&hst.occupancy, 10, hgram_opts);
cpu_fprintf(f, "TB hash occupancy %0.2f%% avg chain occ. Histogram: %s\n",
qdist_avg(&hst.occupancy) * 100, hgram);
g_free(hgram);
hgram_opts = QDIST_PR_BORDER | QDIST_PR_LABELS;
hgram_bins = qdist_xmax(&hst.chain) - qdist_xmin(&hst.chain);
if (hgram_bins > 10) {
hgram_bins = 10;
} else {
hgram_bins = 0;
hgram_opts |= QDIST_PR_NODECIMAL | QDIST_PR_NOBINRANGE;
}
hgram = qdist_pr(&hst.chain, hgram_bins, hgram_opts);
cpu_fprintf(f, "TB hash avg chain %0.3f buckets. Histogram: %s\n",
qdist_avg(&hst.chain), hgram);
g_free(hgram);
}
void dump_exec_info(FILE *f, fprintf_function cpu_fprintf)
{
int i, target_code_size, max_target_code_size;
int direct_jmp_count, direct_jmp2_count, cross_page;
TranslationBlock *tb;
struct qht_stats hst;
uint32_t hgram_opts;
size_t hgram_bins;
char *hgram;
target_code_size = 0;
max_target_code_size = 0;
@ -1724,34 +1759,7 @@ void dump_exec_info(FILE *f, fprintf_function cpu_fprintf)
tcg_ctx.tb_ctx.nb_tbs : 0);
qht_statistics_init(&tcg_ctx.tb_ctx.htable, &hst);
cpu_fprintf(f, "TB hash buckets %zu/%zu (%0.2f%% head buckets used)\n",
hst.used_head_buckets, hst.head_buckets,
(double)hst.used_head_buckets / hst.head_buckets * 100);
hgram_opts = QDIST_PR_BORDER | QDIST_PR_LABELS;
hgram_opts |= QDIST_PR_100X | QDIST_PR_PERCENT;
if (qdist_xmax(&hst.occupancy) - qdist_xmin(&hst.occupancy) == 1) {
hgram_opts |= QDIST_PR_NODECIMAL;
}
hgram = qdist_pr(&hst.occupancy, 10, hgram_opts);
cpu_fprintf(f, "TB hash occupancy %0.2f%% avg chain occ. Histogram: %s\n",
qdist_avg(&hst.occupancy) * 100, hgram);
g_free(hgram);
hgram_opts = QDIST_PR_BORDER | QDIST_PR_LABELS;
hgram_bins = qdist_xmax(&hst.chain) - qdist_xmin(&hst.chain);
if (hgram_bins > 10) {
hgram_bins = 10;
} else {
hgram_bins = 0;
hgram_opts |= QDIST_PR_NODECIMAL | QDIST_PR_NOBINRANGE;
}
hgram = qdist_pr(&hst.chain, hgram_bins, hgram_opts);
cpu_fprintf(f, "TB hash avg chain %0.3f buckets. Histogram: %s\n",
qdist_avg(&hst.chain), hgram);
g_free(hgram);
print_qht_statistics(f, cpu_fprintf, hst);
qht_statistics_destroy(&hst);
cpu_fprintf(f, "\nStatistics:\n");

7
util/qht.c
View File

@ -789,11 +789,16 @@ void qht_statistics_init(struct qht *ht, struct qht_stats *stats)
map = atomic_rcu_read(&ht->map);
stats->head_buckets = map->n_buckets;
stats->used_head_buckets = 0;
stats->entries = 0;
qdist_init(&stats->chain);
qdist_init(&stats->occupancy);
/* bail out if the qht has not yet been initialized */
if (unlikely(map == NULL)) {
stats->head_buckets = 0;
return;
}
stats->head_buckets = map->n_buckets;
for (i = 0; i < map->n_buckets; i++) {
struct qht_bucket *head = &map->buckets[i];