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cache: move open to thread pool

Ka-Hing Cheung via nginx-devel
August 07, 2018 05:28PM
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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Subject Author Views Posted

cache: move open to thread pool

Ka-Hing Cheung via nginx-devel 490 August 07, 2018 05:28PM

Re: cache: move open to thread pool

Maxim Dounin 85 August 08, 2018 02:18PM

RE: cache: move open to thread pool

erankor 67 August 08, 2018 03:46PM

Re: cache: move open to thread pool

Ka-Hing Cheung via nginx-devel 50 August 27, 2018 06:00PM

RE: cache: move open to thread pool

erankor 54 August 28, 2018 05:18AM

Re: cache: move open to thread pool

Ka-Hing Cheung via nginx-devel 66 August 09, 2018 05:44PM

Re: cache: move open to thread pool

Maxim Dounin 64 August 10, 2018 07:42AM

Re: cache: move open to thread pool

Ka-Hing Cheung via nginx-devel 44 August 27, 2018 05:40PM

Re: cache: move open to thread pool

Maxim Dounin 62 September 03, 2018 12:10PM

Re: cache: move open to thread pool

Ka-Hing Cheung via nginx-devel 46 September 04, 2018 08:00PM

Re: cache: move open to thread pool

Maxim Dounin 52 September 13, 2018 02:12PM

Re: cache: move open to thread pool

Roman Arutyunyan 85 October 04, 2018 05:34AM

Re: cache: move open to thread pool

Roman Arutyunyan 49 November 01, 2018 08:30AM

Re: cache: move open to thread pool

Maxim Konovalov 39 November 01, 2018 12:08PM

Re: cache: move open to thread pool

Maxim Konovalov 47 November 08, 2018 09:20AM

Re: cache: move open to thread pool

Ka-Hing Cheung via nginx-devel 32 November 15, 2018 05:54PM

Re: cache: move open to thread pool

Maxim Konovalov 37 November 16, 2018 04:12AM

Re: cache: move open to thread pool

Maxim Konovalov 26 December 05, 2018 04:44AM



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