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authorbauerchen <bauerchen@tencent.com>2020-02-11 17:10:35 +0800
committerPaolo Bonzini <pbonzini@redhat.com>2020-02-25 09:18:01 +0100
commit037fb5eb3941c80a2b7c36a843e47207ddb004d4 (patch)
tree996d02a0c4e3ec1fa92b0ca3838430c48e56edcf
parent920d557e5ae58671d335acbcfba3f9a97a02911c (diff)
downloadqemu-arm-037fb5eb3941c80a2b7c36a843e47207ddb004d4.tar.gz
mem-prealloc: optimize large guest startup
[desc]: Large memory VM starts slowly when using -mem-prealloc, and there are some areas to optimize in current method; 1、mmap will be used to alloc threads stack during create page clearing threads, and it will attempt mm->mmap_sem for write lock, but clearing threads have hold read lock, this competition will cause threads createion very slow; 2、methods of calcuating pages for per threads is not well;if we use 64 threads to split 160 hugepage,63 threads clear 2page,1 thread clear 34 page,so the entire speed is very slow; to solve the first problem,we add a mutex in thread function,and start all threads when all threads finished createion; and the second problem, we spread remainder to other threads,in situation that 160 hugepage and 64 threads, there are 32 threads clear 3 pages,and 32 threads clear 2 pages. [test]: 320G 84c VM start time can be reduced to 10s 680G 84c VM start time can be reduced to 18s Signed-off-by: bauerchen <bauerchen@tencent.com> Reviewed-by: Pan Rui <ruippan@tencent.com> Reviewed-by: Ivan Ren <ivanren@tencent.com> [Simplify computation of the number of pages per thread. - Paolo] Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
-rw-r--r--util/oslib-posix.c32
1 files changed, 24 insertions, 8 deletions
diff --git a/util/oslib-posix.c b/util/oslib-posix.c
index 5a291cc982..897e8f3ba6 100644
--- a/util/oslib-posix.c
+++ b/util/oslib-posix.c
@@ -76,6 +76,10 @@ static MemsetThread *memset_thread;
static int memset_num_threads;
static bool memset_thread_failed;
+static QemuMutex page_mutex;
+static QemuCond page_cond;
+static bool threads_created_flag;
+
int qemu_get_thread_id(void)
{
#if defined(__linux__)
@@ -403,6 +407,17 @@ static void *do_touch_pages(void *arg)
MemsetThread *memset_args = (MemsetThread *)arg;
sigset_t set, oldset;
+ /*
+ * On Linux, the page faults from the loop below can cause mmap_sem
+ * contention with allocation of the thread stacks. Do not start
+ * clearing until all threads have been created.
+ */
+ qemu_mutex_lock(&page_mutex);
+ while(!threads_created_flag){
+ qemu_cond_wait(&page_cond, &page_mutex);
+ }
+ qemu_mutex_unlock(&page_mutex);
+
/* unblock SIGBUS */
sigemptyset(&set);
sigaddset(&set, SIGBUS);
@@ -451,27 +466,28 @@ static inline int get_memset_num_threads(int smp_cpus)
static bool touch_all_pages(char *area, size_t hpagesize, size_t numpages,
int smp_cpus)
{
- size_t numpages_per_thread;
- size_t size_per_thread;
+ size_t numpages_per_thread, leftover;
char *addr = area;
int i = 0;
memset_thread_failed = false;
+ threads_created_flag = false;
memset_num_threads = get_memset_num_threads(smp_cpus);
memset_thread = g_new0(MemsetThread, memset_num_threads);
- numpages_per_thread = (numpages / memset_num_threads);
- size_per_thread = (hpagesize * numpages_per_thread);
+ numpages_per_thread = numpages / memset_num_threads;
+ leftover = numpages % memset_num_threads;
for (i = 0; i < memset_num_threads; i++) {
memset_thread[i].addr = addr;
- memset_thread[i].numpages = (i == (memset_num_threads - 1)) ?
- numpages : numpages_per_thread;
+ memset_thread[i].numpages = numpages_per_thread + (i < leftover);
memset_thread[i].hpagesize = hpagesize;
qemu_thread_create(&memset_thread[i].pgthread, "touch_pages",
do_touch_pages, &memset_thread[i],
QEMU_THREAD_JOINABLE);
- addr += size_per_thread;
- numpages -= numpages_per_thread;
+ addr += memset_thread[i].numpages * hpagesize;
}
+ threads_created_flag = true;
+ qemu_cond_broadcast(&page_cond);
+
for (i = 0; i < memset_num_threads; i++) {
qemu_thread_join(&memset_thread[i].pgthread);
}