[Bug libc/207] ucontext is very slow.

["a dot darovskikh at compassplus dot ru" <sourceware-bugzilla at sources dot redhat dot com>]

------- Additional Comments From a dot darovskikh at compassplus dot ru  2004-06-09 04:30 -------
Subject: Re:  ucontext is very slow.

On Tuesday 08 June 2004 20:38, jakub at redhat dot com wrote:
> ------- Additional Comments From jakub at redhat dot com  2004-06-08 14:38
> ------- Hardly.
> More than 50% of the time is spent in sigprocmask syscalls, which are
> needed (the program can change its signal mask any time and this needs to
> be preserved, caching current signal mask in userland would be a huge can
> of problems and slowdowns for little gain).
> The other big part of the total time is spent on saving/restoring FPU state
> (again, swapcontext must do this) and that's about it.
>
> Why aren't you using real threads instead?

This is because we use thousands so-called "tasks", which access on the same 
"tree". If we implement it using real threads, they will use complex 
synchronization, which will take much more time than the real work. This is 
why we need cooperative multitasking. There are some more complex reasons for 
this, so I'm afraid, we will not able to use real threads. Indeed, we do use 
it, but it's for external things, like database connections.

Is it possible to avoid sigprocmask syscalls and FPU things? We do not use it.

Maybe it's possible to take this code and remove those calls from it? Or use 
something like setjmp/longjmp? I tried last one, but timings were even worse.

Alexander Darovsky.


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http://sources.redhat.com/bugzilla/show_bug.cgi?id=207

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