On 3/22/07, Ajay Singh (ajaysi) <ajaysi@xxxxxxxxx> wrote:
> -----Original Message----- > From: kernelnewbies-bounce@xxxxxxxxxxxx > [mailto:kernelnewbies-bounce@xxxxxxxxxxxx] On Behalf Of Rajat Jain > Sent: Thursday, March 22, 2007 6:43 AM > To: Arjan van de Ven > Cc: anubhav rakshit; kernel mail; newbie > Subject: Re: Need for a new spinlock API? > > Hi Arjan, > > > > > > We often have a case where a driver wants to access its data > > > > > structure in process context as well as in interrupt > context (in > > > > > its ISR). In such scenarios, we generally use > > > > > spin_lock_irqsave() to grab the lock as well as > disable all the > > > > > local interrupts. AFAIK, disabling of local interrupts is > > > > > required so as to avoid running your ISR (which needs > the lock) > > > > > while process context is holding the lock. However, this also > > > > > disables any other ISRs (which DO NOT need the lock) > on the local processor. > > > > > > > > > > Isn't this sub-optimal? Shouldn't there be a finer > grained locking? > > > > > > > > actually it's optimal. > > > how is it optimal,when all you require is to disable > just one particular IRQ? > > > > because if you don't disable all you increase hold times, which > > increases contention. Contention is BAD. > > Do you mean the lock hold time here? How is lock hold time > affected by whether we disable just one or all the irqs? The lock hold time may increase if you are in one ISR holding a lock and some other interrupt occurs. Processor will now call ISR linked to that interrupt (nested interrupts) assuming that priority of newly arrived interrupt is more.
Yes, but isn't that desired? Because the newly arrived interrupt is of higher priority than the currently executing ISR and it doesn't need any lock at all, shouldn't the new ISR experience a lesser interrupt latency (executed before the current ISR finishes)?
> > Secondly, is it possible AT ALL to disable a particular irq > at the local CPU? It depends on the interrupt controller implementation in h/w. In most cases it should be possible. Most of them are quite programmable where you can mask out, disable, enable any interrupt line, set the priority of the interrupt line.
So we can disable a single interrupt ONLY for the local CPU (leaving it enabled for other CPUs), right? Thanks, Rajat - To unsubscribe from this list: send the line "unsubscribe linux-newbie" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.linux-learn.org/faqs
