commit 0bcfefa040abdff674047c15701d237ff16a5f2b
Author: Ka-Hing Cheung <kahing@cloudflare.com>
Date: Fri Aug 3 13:37:58 2018 -0700

move open to thread pool

At cloudflare we found that open() can block a long time, especially
at p99 and p999. Moving it to thread pool improved overall p99 by 6x
or so during peak time.

This has the side effect of disabling nginx's open_file_cache when
"aio threads" is turned on. For us we found that to have no impact
(probably because we have way too many files for open file cache to
be effective anyway).

thread pool does increase CPU usage somewhat but we have not measured
difference in CPU usage for stock "aio threads" compared to after this
patch.

Only the cache hit open() is moved to thread pool.

We wrote more about it here:
https://blog.cloudflare.com/how-we-scaled-nginx-and-saved-the-world-54-years-every-day/

diff --git src/core/ngx_open_file_cache.c src/core/ngx_open_file_cache.c
index b23ee78d..9177ebfd 100644
--- src/core/ngx_open_file_cache.c
+++ src/core/ngx_open_file_cache.c
@@ -35,8 +35,6 @@ static ngx_fd_t ngx_open_file_wrapper(ngx_str_t *name,
ngx_int_t access, ngx_log_t *log);
static ngx_int_t ngx_file_info_wrapper(ngx_str_t *name,
ngx_open_file_info_t *of, ngx_file_info_t *fi, ngx_log_t *log);
-static ngx_int_t ngx_open_and_stat_file(ngx_str_t *name,
- ngx_open_file_info_t *of, ngx_log_t *log);
static void ngx_open_file_add_event(ngx_open_file_cache_t *cache,
ngx_cached_open_file_t *file, ngx_open_file_info_t *of, ngx_log_t *log);
static void ngx_open_file_cleanup(void *data);
@@ -836,7 +834,7 @@ ngx_file_info_wrapper(ngx_str_t *name,
ngx_open_file_info_t *of,
}


-static ngx_int_t
+ngx_int_t
ngx_open_and_stat_file(ngx_str_t *name, ngx_open_file_info_t *of,
ngx_log_t *log)
{
diff --git src/core/ngx_open_file_cache.h src/core/ngx_open_file_cache.h
index d119c129..94b4d552 100644
--- src/core/ngx_open_file_cache.h
+++ src/core/ngx_open_file_cache.h
@@ -124,6 +124,8 @@ ngx_open_file_cache_t
*ngx_open_file_cache_init(ngx_pool_t *pool,
ngx_uint_t max, time_t inactive);
ngx_int_t ngx_open_cached_file(ngx_open_file_cache_t *cache, ngx_str_t *name,
ngx_open_file_info_t *of, ngx_pool_t *pool);
+ngx_int_t ngx_open_and_stat_file(ngx_str_t *name,
+ ngx_open_file_info_t *of, ngx_log_t *log);


#endif /* _NGX_OPEN_FILE_CACHE_H_INCLUDED_ */
diff --git src/http/ngx_http_cache.h src/http/ngx_http_cache.h
index f9e96640..2910f6a1 100644
--- src/http/ngx_http_cache.h
+++ src/http/ngx_http_cache.h
@@ -114,6 +114,7 @@ struct ngx_http_cache_s {
unsigned exists:1;
unsigned temp_file:1;
unsigned purged:1;
+ unsigned opening:1;
unsigned reading:1;
unsigned secondary:1;
unsigned background:1;
diff --git src/http/ngx_http_file_cache.c src/http/ngx_http_file_cache.c
index 56866fa4..9cb110bf 100644
--- src/http/ngx_http_file_cache.c
+++ src/http/ngx_http_file_cache.c
@@ -18,6 +18,10 @@ static void
ngx_http_file_cache_lock_wait(ngx_http_request_t *r,
ngx_http_cache_t *c);
static ngx_int_t ngx_http_file_cache_read(ngx_http_request_t *r,
ngx_http_cache_t *c);
+static ngx_int_t ngx_http_file_cache_aio_open(ngx_http_request_t *r,
+ ngx_http_cache_t *c, ngx_int_t *rv);
+static ngx_int_t ngx_http_file_cache_do_aio_open(ngx_http_request_t *r,
+ ngx_http_cache_t *c, ngx_open_file_info_t *of, ngx_int_t *rv);
static ssize_t ngx_http_file_cache_aio_read(ngx_http_request_t *r,
ngx_http_cache_t *c);
#if (NGX_HAVE_FILE_AIO)
@@ -268,9 +272,7 @@ ngx_http_file_cache_open(ngx_http_request_t *r)
ngx_uint_t test;
ngx_http_cache_t *c;
ngx_pool_cleanup_t *cln;
- ngx_open_file_info_t of;
ngx_http_file_cache_t *cache;
- ngx_http_core_loc_conf_t *clcf;

c = r->cache;

@@ -278,6 +280,10 @@ ngx_http_file_cache_open(ngx_http_request_t *r)
return NGX_AGAIN;
}

+ if (c->opening) {
+ return ngx_http_file_cache_aio_open(r, c, &rv);
+ }
+
if (c->reading) {
return ngx_http_file_cache_read(r, c);
}
@@ -343,23 +349,33 @@ ngx_http_file_cache_open(ngx_http_request_t *r)
goto done;
}

- clcf = ngx_http_get_module_loc_conf(r, ngx_http_core_module);
+ return ngx_http_file_cache_aio_open(r, c, &rv);

- ngx_memzero(&of, sizeof(ngx_open_file_info_t));
+done:

- of.uniq = c->uniq;
- of.valid = clcf->open_file_cache_valid;
- of.min_uses = clcf->open_file_cache_min_uses;
- of.events = clcf->open_file_cache_events;
- of.directio = NGX_OPEN_FILE_DIRECTIO_OFF;
- of.read_ahead = clcf->read_ahead;
+ if (rv == NGX_DECLINED) {
+ return ngx_http_file_cache_lock(r, c);
+ }

- if (ngx_open_cached_file(clcf->open_file_cache, &c->file.name,
&of, r->pool)
- != NGX_OK)
- {
- switch (of.err) {
+ return rv;
+}
+
+static ngx_int_t
+ngx_http_file_cache_aio_open(ngx_http_request_t *r, ngx_http_cache_t *c,
+ ngx_int_t *rv)
+{
+ ngx_int_t rc;
+ ngx_open_file_info_t of;
+ ngx_http_file_cache_t *cache = c->file_cache;

- case 0:
+ rc = ngx_http_file_cache_do_aio_open(r, c, &of, rv);
+ if (rc == NGX_AGAIN) {
+ return rc;
+ }
+
+ if (rc != NGX_OK) {
+ switch (of.err) {
+ case NGX_OK:
return NGX_ERROR;

case NGX_ENOENT:
@@ -391,14 +407,13 @@ ngx_http_file_cache_open(ngx_http_request_t *r)

done:

- if (rv == NGX_DECLINED) {
+ if (*rv == NGX_DECLINED) {
return ngx_http_file_cache_lock(r, c);
}

- return rv;
+ return *rv;
}

-
static ngx_int_t
ngx_http_file_cache_lock(ngx_http_request_t *r, ngx_http_cache_t *c)
{
@@ -663,6 +678,127 @@ ngx_http_file_cache_read(ngx_http_request_t *r,
ngx_http_cache_t *c)
}


+#if (NGX_THREADS)
+typedef struct {
+ ngx_str_t name;
+ ngx_pool_t *pool;
+ ngx_open_file_info_t of;
+ ngx_int_t rv;
+} ngx_thread_file_open_ctx_t;
+
+static void
+ngx_http_file_cache_thread_open_handler(void *data, ngx_log_t *log)
+{
+ ngx_thread_file_open_ctx_t *ctx = data;
+ ngx_pool_t *pool = ctx->pool;
+ ngx_open_file_info_t *of = &ctx->of;
+ ngx_pool_cleanup_t *cln;
+ ngx_pool_cleanup_file_t *clnf;
+ ngx_int_t rc;
+
+ ngx_log_debug0(NGX_LOG_DEBUG_CORE, log, 0, "thread read handler");
+
+ cln = ngx_pool_cleanup_add(pool, sizeof(ngx_pool_cleanup_file_t));
+ if (cln == NULL) {
+ ctx->of.err = NGX_ERROR;
+ return;
+ }
+
+ of->fd = NGX_INVALID_FILE;
+
+ rc = ngx_open_and_stat_file(&ctx->name, of, pool->log);
+ if (rc == NGX_OK && !of->is_dir) {
+ cln->handler = ngx_pool_cleanup_file;
+ clnf = cln->data;
+
+ clnf->fd = of->fd;
+ clnf->name = ctx->name.data;
+ clnf->log = pool->log;
+ }
+}
+
+
+static ngx_int_t
+ngx_http_file_cache_thread_open(ngx_http_cache_t *c, ngx_open_file_info_t *of,
+ ngx_int_t *rv, ngx_pool_t *pool)
+{
+ ngx_thread_task_t *task;
+ ngx_thread_file_open_ctx_t *ctx;
+ ngx_file_t *file = &c->file;
+
+ task = file->thread_task;
+
+ if (task == NULL) {
+ task = ngx_thread_task_alloc(pool, sizeof(ngx_thread_file_open_ctx_t));
+ if (task == NULL) {
+ return NGX_ERROR;
+ }
+
+ file->thread_task = task;
+ }
+
+ ctx = task->ctx;
+
+ if (task->event.complete) {
+ task->event.complete = 0;
+
+ *of = ctx->of;
+ *rv = ctx->rv;
+ return of->err;
+ }
+
+ task->handler = ngx_http_file_cache_thread_open_handler;
+
+ ctx->pool = pool;
+ ctx->name = file->name;
+ ctx->of = *of;
+ ctx->rv = *rv;
+
+ if (file->thread_handler(task, file) != NGX_OK) {
+ return NGX_ERROR;
+ }
+
+ return NGX_AGAIN;
+}
+#endif
+
+static ngx_int_t
+ngx_http_file_cache_do_aio_open(ngx_http_request_t *r, ngx_http_cache_t *c,
+ ngx_open_file_info_t *of, ngx_int_t *rv)
+{
+ ngx_http_core_loc_conf_t *clcf;
+
+ clcf = ngx_http_get_module_loc_conf(r, ngx_http_core_module);
+
+ ngx_memzero(of, sizeof(ngx_open_file_info_t));
+
+ of->uniq = c->uniq;
+ of->valid = clcf->open_file_cache_valid;
+ of->min_uses = clcf->open_file_cache_min_uses;
+ of->events = clcf->open_file_cache_events;
+ of->directio = NGX_OPEN_FILE_DIRECTIO_OFF;
+ of->read_ahead = clcf->read_ahead;
+
+#if (NGX_THREADS)
+ if (clcf->aio == NGX_HTTP_AIO_THREADS) {
+ ngx_int_t rc;
+
+ c->file.thread_task = c->thread_task;
+ c->file.thread_handler = ngx_http_cache_thread_handler;
+ c->file.thread_ctx = r;
+
+ rc = ngx_http_file_cache_thread_open(c, of, rv, r->pool);
+
+ c->thread_task = c->file.thread_task;
+ c->opening = (rc == NGX_AGAIN);
+
+ return rc;
+ }
+#endif
+
+ return ngx_open_cached_file(clcf->open_file_cache, &c->file.name,
of, r->pool);
+}
+
static ssize_t
ngx_http_file_cache_aio_read(ngx_http_request_t *r, ngx_http_cache_t *c)
{
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