On 10/24/07, Vernooy, C.P. - SPLXM <[EMAIL PROTECTED]> wrote: > > > > > > I think what the manual says is the same as what you said. In a MP > system, a > > disabled loop is observed as a spin loop by other processors. > > This is not exactly true: > A disabled loop by itsself will not generate a problem. However, other > processors will regularly want to talk to the disabled processor, via > the SIGP instruction. The calling processor will spin (in a disabled > loop, therefor spin loop) waiting for an answer. The disabled called > processor will of course not answer and the calling processor will > detect this and generate an "excessive spinloop time out" condition. So > the spinloop is a normal, short duration, situation; an excisive > spinloop timeout is a condition detected by an active processor, where > an other processor does not answer. This can be for many reasons, being > disabled, hardware problems etc. etc. > > Have a look at Initialization and Tuning Reference, member EXCPATxx, for > more information on spinloops.
This leads me to reconsider my understanding about the process of getting a spin lock. I used to think what SETLOCK does is just keeping on check the lockword and running disabled. Then, what is the difference between a spin loop and a disabled loop? So my guess is, what SETLOCK does is a 'timed disabled loop'. That is, most of the time it'll loop disabled but not forever. It will enable the processor regularly thus an excessive spin loop can be detected and handled by system. Did I miss something here? I have another question about RB queue/chain. (A little off-topic but at least it is involved in dispatching process -_- ) Here is a RB chain after a new RB is added: TCB <-- RB1 <-- RB2 <-- RB3 I think RB1 is the oldest and RB3 is the newest but is it true? Then this TCB is dispatched and the RB pointed by TCBRBP will be executed. Which one? I think it should be RB3 ( the newest) but I'm not sure. Thanks, Johnny ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
