Calling FFI-backed function returns 0 time elapsed

rwag · 2015-08-31T22:42:53+00:00

Hello! On Mon, Aug 31, 2015 at 7:53 AM, estebanSannin wrote: > local line, err = sock:receive("*a") Oh, BTW, it's not a good practice to use &...

Calling FFI-backed function returns 0 time elapsed

rwag

I am running the 1.9.3.1 version of OpenResty on the Mac.

When I call an lua-function that is FFI-backed I am finding the elapsed-time is coming back as 0 or some other extremely low number.

====

local start = ngx.now()

package.ffiBackedCall()

local stop = ngx.now()

====

This appears to happen even if I put a sleep for 2 seconds in the C code. I tried that on OpenResty 1.7.10.2.

Is there something I missed on this?

doujiang24

hi,

ngx.now just return nginx cached time [1]

You can forcibly update the Nginx time cache by calling ngx.update_time[2] first.

1. http://wiki.nginx.org/HttpLuaModule#ngx.now

2. http://wiki.nginx.org/HttpLuaModule#ngx.update_time

2015-08-31 22:42 GMT+08:00 Rollin Crittendon <r...@rwag.net>:

I am running the 1.9.3.1 version of OpenResty on the Mac.

When I call an lua-function that is FFI-backed I am finding the elapsed-time is coming back as 0 or some other extremely low number.

====
local start = ngx.now()
package.ffiBackedCall()
local stop = ngx.now()
====

This appears to happen even if I put a sleep for 2 seconds in the C code. I tried that on OpenResty 1.7.10.2.

Is there something I missed on this?

.

rwag

Thank you Dejiang,

I just tried the call and it does appear to get me the actual time.

I was reading the link for it, and am wondering if calling that is an issue if I do that say 300 or so times a second per process.

On Monday, August 31, 2015 at 11:01:20 AM UTC-4, DeJiang Zhu wrote:

hi,

ngx.now just return nginx cached time [1]
You can forcibly update the Nginx time cache by calling ngx.update_time[2] first.

1. http://wiki.nginx.org/HttpLuaModule#ngx.now
2. http://wiki.nginx.org/HttpLuaModule#ngx.update_time

2015-08-31 22:42 GMT+08:00 Rollin Crittendon <rw...@rwag.net>:
I am running the 1.9.3.1 version of OpenResty on the Mac.

When I call an lua-function that is FFI-backed I am finding the elapsed-time is coming back as 0 or some other extremely low number.

====
local start = ngx.now()
package.ffiBackedCall()
local stop = ngx.now()
====

This appears to happen even if I put a sleep for 2 seconds in the C code. I tried that on OpenResty 1.7.10.2.

Is there something I missed on this?

.

rpaprocki

It depends on your use case. Each call to ngx.update_time() requires a syscall, which can be detrimental to performance.

If you just want to profile how much time is spent in lua land, you may want to look at https://github.com/openresty/nginx-systemtap-toolkit, which can get you more reliable timing results without needing to constantly call out to the kernel from within your app.

Keep in mind that nginx only maintains millisecond precision when tracking time, even when calling ngx.update_time; see https://groups.google.com/forum/m/#!topic/openresty-en/_OnAxHSB61I for a bit more discussion on this.

Hope this helps!

Sent from my iPhone

On Aug 31, 2015, at 08:16, Rollin Crittendon <r...@rwag.net> wrote:

Thank you Dejiang,

I just tried the call and it does appear to get me the actual time.

I was reading the link for it, and am wondering if calling that is an issue if I do that say 300 or so times a second per process.

On Monday, August 31, 2015 at 11:01:20 AM UTC-4, DeJiang Zhu wrote:
hi,

ngx.now just return nginx cached time [1]
You can forcibly update the Nginx time cache by calling ngx.update_time[2] first.

1. http://wiki.nginx.org/HttpLuaModule#ngx.now
2. http://wiki.nginx.org/HttpLuaModule#ngx.update_time

2015-08-31 22:42 GMT+08:00 Rollin Crittendon <rw...@rwag.net>:
I am running the 1.9.3.1 version of OpenResty on the Mac.

When I call an lua-function that is FFI-backed I am finding the elapsed-time is coming back as 0 or some other extremely low number.

====
local start = ngx.now()
package.ffiBackedCall()
local stop = ngx.now()
====

This appears to happen even if I put a sleep for 2 seconds in the C code. I tried that on OpenResty 1.7.10.2.

Is there something I missed on this?

.