# Help with AIO **URL:** \ **Category:** NGINX\ **Created:** [September 6, 2011, 12:22am UTC](https://www.ruby-forum.com/t/help-with-aio/211502 "2011-09-06T00:22:15Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![luislavena](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/0ea827/32.png) [@luislavena](https://www.ruby-forum.com/u/luislavena)\ **Post date:** [September 6, 2011, 12:22am UTC](https://www.ruby-forum.com/t/help-with-aio/211502/1 "2011-09-06T00:22:15Z")
Hi I configured Nginx with \*aio \*mode \*on \*and 1 _worker process_ In benchmarking I saw limit of 1024 concurrent sessions even configured to 4096 _worker connections_ When I looked in the source code I could see that io\_setup is called with fix value of 1024 max events can anyone please explain me the hard coded limit Is it OK to change it or it is derived from other limit I am not aware of any help will be appreciated thanks Hagai – _Hagai A._ Qwilt | Work: +972-72-2221644| Mobile: +972-54-4895656 | removed\_email\_address@domain.invalid[removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) ---
**Author:** ![Hagai\_A](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/a9a28c/32.png) [@Hagai\_A](https://www.ruby-forum.com/u/Hagai_A)\ **Post date:** [September 6, 2011, 9:34am UTC](https://www.ruby-forum.com/t/help-with-aio/211502/2 "2011-09-06T09:34:14Z")
Hello! On Tue, Sep 06, 2011 at 01:21:00AM +0300, Hagai A. wrote: > Hi > > I configured Nginx with \*aio \*mode \*on \*and 1 _worker process_ > In benchmarking I saw limit of 1024 concurrent sessions even configured to > 4096 _worker connections_ Sure it’s not limitation of the benchmarking tool you use? Most tools out there use select() and hence limited to 1024 concurrent connections. > When I looked in the source code I could see that io\_setup is called with > fix value of 1024 max events > can anyone please explain me the hard coded limit > Is it OK to change it or it is derived from other limit I am not aware of > any help will be appreciated io\_setup() maxevents is a limit on number of aio requests allowed to be submitted simulteneously; if nginx hits this limit, it will fallback to normal blocking read. If you are going to change it, make sure to keep total for all processes lower than /proc/sys/fs/aio-max-nr. Maxim D. ---
**Author:** ![Hagai\_A](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/a9a28c/32.png) [@Hagai\_A](https://www.ruby-forum.com/u/Hagai_A)\ **Post date:** [September 6, 2011, 9:47am UTC](https://www.ruby-forum.com/t/help-with-aio/211502/3 "2011-09-06T09:47:50Z")
Thanks a lot I will try it On Tue, Sep 6, 2011 at 9:33 AM, Maxim D. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > nginx mailing list > [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) > [mailman.nginx.org archive](http://mailman.nginx.org/mailman/listinfo/nginx) – _Hagai A._ Qwilt | Work: +972-72-2221644| Mobile: +972-54-4895656 | [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)[removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) ---
**Author:** ![Hagai\_A](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/a9a28c/32.png) [@Hagai\_A](https://www.ruby-forum.com/u/Hagai_A)\ **Post date:** [September 15, 2011, 4:22pm UTC](https://www.ruby-forum.com/t/help-with-aio/211502/4 "2011-09-15T16:22:38Z")
Hi ## When benchmarking AIO read, I reached more than 1024 concurrent Async IO 1. I saw a weird error log 2. Nginx did not fallback to regular blocking read I looked on the source code – src/os/unix/ngx\_linux\_aio\_read.c line:105 and I think there is a problem in errno handling // Current Code //---------------------------------------------------------------------------- \*n = io\_submit(ngx\_aio\_ctx, 1, piocb); ``` if (n == 1) { ev->active = 1; ev->ready = 0; ev->complete = 0; return NGX_AGAIN; } n = -n; ``` \<---------------------------------------------------------?? ``` if (n == NGX_EAGAIN) { return ngx_read_file(file, buf, size, offset); } ngx_log_error(NGX_LOG_CRIT, file->log, n, "io_submit(\"%V\") failed", &file->name); if (n == NGX_ENOSYS) { ngx_file_aio = 0; return ngx_read_file(file, buf, size, offset); } return NGX_ERROR;* ``` // I think it should be //---------------------------------------------------------------------------- \*n = io\_submit(ngx\_aio\_ctx, 1, piocb); ``` if (n == 1) { ev->active = 1; ev->ready = 0; ev->complete = 0; return NGX_AGAIN; } if (n == 0) { ngx_log_error(NGX_LOG_CRIT, file->log, 0, "io_submit(\"%V\") failed - 0 - I/O request blocks", ``` &file-\>name); ``` return NGX_ERROR; } else { n = errno; } ``` - - if (n== NGX\_EAGAIN) { return ngx\_read\_file(file, buf, size, offset); } ngx\_log\_error(NGX\_LOG\_CRIT, file-\>log, n, “io\_submit("%V") failed”, &file-\>name); if (n== NGX\_ENOSYS) { ngx\_file\_aio = 0; return ngx\_read\_file(file, buf, size, offset); } return NGX\_ERROR;\* //---------------------------------------------------------------------------- your help will be appreciated Thanks Hagai On Tue, Sep 6, 2011 at 9:33 AM, Maxim D. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > nginx mailing list > [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) > [mailman.nginx.org archive](http://mailman.nginx.org/mailman/listinfo/nginx) – _Hagai A._ Qwilt | Work: +972-72-2221644| Mobile: +972-54-4895656 | [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)[removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) ---
**Author:** ![Hagai\_A](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/a9a28c/32.png) [@Hagai\_A](https://www.ruby-forum.com/u/Hagai_A)\ **Post date:** [September 16, 2011, 12:39pm UTC](https://www.ruby-forum.com/t/help-with-aio/211502/5 "2011-09-16T12:39:22Z")
On Thu, Sep 15, 2011 at 04:21:44PM +0200, Hagai A. wrote: > //---------------------------------------------------------------------------- > n = -n; \<---------------------------------------------------------?? > Thank you, this is a bug. I confused this with \_syscall(2). – Igor S. ---
**Author:** ![Hagai\_A](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/a9a28c/32.png) [@Hagai\_A](https://www.ruby-forum.com/u/Hagai_A)\ **Post date:** [September 17, 2011, 12:59pm UTC](https://www.ruby-forum.com/t/help-with-aio/211502/6 "2011-09-17T12:59:20Z")
On Fri, Sep 16, 2011 at 06:10:02PM +0400, Igor S. wrote: > > > ``` > > > } > > > > > > ``` > > Also I’m going to introduce the directive: > > events { > worker\_aio\_events 100; > } > > to set how much aio events worker may request to the kernel. > I’m going to set default value to 32 events per worker. > Currenly this value is hardcoded to 1024 and it seems it is too large, > since default /proc/sys/fs/aio-max-nr value is 65536 and this means > that you can run no more than 64 workers. I think it should be renamed to events { worker\_aio\_requests 100; } – Igor S. ---
**Author:** ![Hagai\_A](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/a9a28c/32.png) [@Hagai\_A](https://www.ruby-forum.com/u/Hagai_A)\ **Post date:** [September 16, 2011, 4:10pm UTC](https://www.ruby-forum.com/t/help-with-aio/211502/7 "2011-09-16T16:10:51Z")
On Fri, Sep 16, 2011 at 02:39:07PM +0400, Igor S. wrote: > > // Current Code > > > > ``` > > n = -n; <---------------------------------------------------------?? > > > > ``` > > Thank you, this is a bug. I confused this with \_syscall(2). Linux AIO fixed in these two commits: [http://trac.nginx.org/nginx/changeset/4130/nginx](http://trac.nginx.org/nginx/changeset/4130/nginx) [http://trac.nginx.org/nginx/changeset/4131/nginx](http://trac.nginx.org/nginx/changeset/4131/nginx) Also I’m going to introduce the directive: events { worker\_aio\_events 100; } to set how much aio events worker may request to the kernel. I’m going to set default value to 32 events per worker. Currenly this value is hardcoded to 1024 and it seems it is too large, since default /proc/sys/fs/aio-max-nr value is 65536 and this means that you can run no more than 64 workers. – Igor S.