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Subject [GitHub] [incubator-nuttx] sebastianene07 commented on pull request #1009: Add support for preemptive scheduling in simulator build
Date Sat, 09 May 2020 14:31:40 GMT

sebastianene07 commented on pull request #1009:
URL: https://github.com/apache/incubator-nuttx/pull/1009#issuecomment-626184887


   > > > @sebastianene07 I stop to review the last several patch because it's better
to reorg your patch into a meaning set. For example, I found serveral patch fix the problem
in the previous one.
   > > > And basically, the better change is enhance up_oneshot.c which is much simple
and get the tickless support free:
   > > > 1.Register alarm timer in up_oneshot.c
   > > > 2.Call back to NuttX in signal action
   > > > 3.Modify up_irq_save/up_irq_restore to disable/enable signal
   > > > I don't think it's nessary to use ucontext API.
   > > 
   > > 
   > > I used ucontext API because it can restore the signal mask after a call to `swapcontext`.
The setjmp/longjmp mechanism doesn't seem to work with signals. Do you think it's better to
close this PR and re-open a different one with the suggested changes ?
   > 
   > But if the irq save/restore work correctly, I think we don't need care about the host
signal logic. The thread in NuttX isn't 1:1 mapping to host thread. The whole NuttX simulator
run on one host thread(main thread) except you enable SMP then we have multiple threads(same
number as Simulated CPUs). The context switch inside NuttX doesn't mean we switch host thread.
From the host view, the thread is still running on the main thread, so I can't understand
why we need save/restore host signal flag here.
   
   We need to care about the host signal logic because when we are executing the timer signal
handler we usually end up altering the signal handler execution flow(by doing a longjmp).
Altering the execution flow of the signal handler without restoring the signal mask may lead
to no further events being served. 


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