Dmitry Adamushko wrote: > > [EMAIL PROTECTED] wrote on 11.11.2005 10:30:26: > > > Hi, > > > > I'm porting an app from RTAI to Xenomai, and when it came to the > > rt_printk function, I had to replace it with plain printk (the > > xnarch_log* functions all use printk). > > > > What I want to know if: > > > > 1- Is totally safe to call the standard kernel printk function from a > > real time task? > > Actually, the adeos/ipipe patches make some changes to the vanilla > kernel's printk() mechanism. > > There are 2 possible modes of printk() being issued from the primary > domain. > > 1) asynchronous: > > all data is written into the protected buffer and the > __ipipe_printk_virq virq is risen for the secondary domain. So the > data will be printed out when the linux gets control next time. > > Although, here is, well, a tiny race because of the fact that the virq > handler doesn't lock a buffer-related data (like __ipipe_printk_fill) > so a loss of data may occur under some circumstances. > > 2) synchronous (IPIPE_SPRINTK_FLAG) > > in this case, a normal linux vprintk() call is issued. Oops, this one, > in turn, calls spin_lock_irqsave(&logbuf_lock, flags); in real-time > context and that lock may be already held by a preempted non-rt task > on the same CPU. > > Houston? :o) > (2) is unacceptable. Losing some data would be acceptable if it is caused by too much printk output, but not because of a race condition. This should be fixed. I guess a simple FIFO with proper locking should be in place. printk would discard data only if there is no space left.
> > > > > 2- Even if it's safe, can it affect the performance of a real time task? > > (or can it block under *any* conceivable condition?) > > It gives some overhead since data must be copied to the buffer and at > that time the interrupts are off. > Blocked? No, if not taking into account a possible "hang up" with the > synchronous mode (ok, as always there is still a hope that I can be > wrong ):) > If you are right, then it's unacceptable. An RT task would be blocked by a non-RT task. > > > > > Thanks. > > > > Nacho. > > > > --- > Best regards, > Dmitry > >------------------------------------------------------------------------ > >No virus found in this incoming message. >Checked by AVG Free Edition. >Version: 7.1.362 / Virus Database: 267.13.0/167 - Release Date: 11/11/2005 > > _______________________________________________ Xenomai-help mailing list Xenomai-help@gna.org https://mail.gna.org/listinfo/xenomai-help
