Re: signal dequeue ...

[Davide Libenzi]

On 22-Jun-2001 Paul Menage wrote:
> In article <[e-mail]>,
> you write:
>>
>>Right, but the remaining signals are still pending.  In your method, the
>>kernel doesn't know which were and which were not actually delivered.
>>
> 
> You could add an SA_MULTIPLE flag to the sigaction() sa_flags, which
> permit the kernel to stack multiple signals up in this way for apps
> that guarantee not to misbehave. In do_signal()/handle_signal(), only
> allow a signal to be stacked on another signal if its handler has
> SA_MULTIPLE set. So non-stackable signals will always be the last
> signal frame of the stack to be entered, and it won't matter if they
> longjmp() out.
> 
> Would the performance improvement from this be worthwhile? I imagine if
> you're handling a lot of SIGIO signals, the ability to batch up several
> signals in a single user/kernel crossing might be of noticeable benefit.

This could be a good idea but before moving a single hair I want to measure the
maximum ( and average ) queue length for rt signals.
In case this will be constantly > 1 to have a multiple signal dispatch will
save a lot of kernel-mode / user-mode switches.
Otherwise this will be files under NAI ( Not An Issue ) :)

- Davide