Re: strange bottleneck with SMB 2.0

[Jeff Layton <jlayton-vpEMnDpepFuMZCB2o+C8xQ@public.gmane.org>]

On Wed, 19 Aug 2015 04:11:31 -0700
Yale Zhang <yzhang1985-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:

> SMB developers/users,
> 
> I'm experiencing a strange bottleneck when my files are mounted as SMB
> 2.0. When I launch  multiple processes in parallel for benchmarking,
> only the 1st one starts, and the rest won't start until the 1st one
> finishes:
> 
> ---------------------------------------test
> programs--------------------------------
> #!/bin/sh
> ./a.out&
> ./a.out&
> ./a.out&
> wait
> 
> a.out is just a C program like this:
> 
> int main()
> {
>   printf("greetings\n");
>   while (true);
>   return 0;
> }
> 
> Apparently, this only affects SMB 2.0. I tried it with SMB 2.1, SMB
> 3.0, & SMB 3.02, and everything starts in parallel as expected.
> 
> I'm assuming SMB 3 and especially SMB 2.1 would share a common
> implementation. How could 2.0 have the problem but not 3? It almost
> seems the bottleneck is a feature instead of a bug?  8(
> 
> Can it still be fixed?
> 
> -Yale

Probably. It'd be interesting to see what the other tasks are blocking
on. After firing up the second one can you run:

    # cat /proc/<pid of second a.out>/stack

...and paste the stack trace here? That should tell us what those other
processes are doing.

-- 
Jeff Layton <jlayton-vpEMnDpepFuMZCB2o+C8xQ@public.gmane.org>