On Mon, Jun 13, 2005 at 03:55:31PM -0400, Robert Story wrote:
> On Mon, 13 Jun 2005 13:49:49 +0200 Thomas wrote:
> TA> while doing performance tuning for my net-snmp-based applications I
> TA> noticed that launching external programs (exec/extend/traphandle)
> TA> currently (5.3.dev) involves the brute-force approach
> TA>
> TA> close(1023) = -1 EBADF (Bad file descriptor)
> TA> close(1022) = -1 EBADF (Bad file descriptor)
> TA> ...
> TA> close(3) = -1 EBADF (Bad file descriptor)
> TA>
> TA> (see agent/mibgroup/util_funcs.c::get_exec_{output,pipes}) which looks
> TA> safe but wasteful. This takes ~0.1 seconds in sum on my system (*a lot*
> TA> in terms of real-time processing and scalability, even within the
> TA> limitations of external apps), probably even worse on systems with a
> TA> higher RLIMIT_NOFILE.
> TA>
> TA> Any thoughts on improving this (e.g. by remembering the open fds)? Or is
> TA> there a good reason to keep it the way it is?
>
> The problem is that we don't know what fds custom modules might have opened,
> and we don't want' to pass them to any script. Probably the safest/most
> efficient way of dealing with this would be for the agent to create a small
> pool (maybe even 1) of child processes, which do nothing but wait for a
> command
> to exec. They close the fds when created, so there is no delay when the exec
> is
> needed. After the exec, the child dies, and the agent creates another. This
> also has the performance advantage of getting the fork out of the way earlier
> too.
I think it would be even better to spawn a child that handles spawning of the
executing child processes, the drawback is that the child would have to be a
subagent of some kind, the gain is that we can control all fds in the subagent
and mark them as close-on-exec once the executing child have been started.
If we go down this path I also suppose that this code could be broken out into
a separate binary as it would work well standalon also.
/MF
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