Avi Kivity wrote: > On 10/28/2009 03:19 PM, Gregory Haskins wrote: >>> Yes, and it also contains the work_struct. >>> >>> What if we make the work_struct (and any additional state) part of the >>> set_atomic() argument list? Does it simplify things? >>> >> Hmmm, that might not, but we could do a kmalloc(GFP_ATOMIC) for such >> parameters. Considering this is just a safety net, perhaps this would >> work fine. >> > > Can't you simply pass the same work_struct from irqfd as we use now? Well, yes, of course, but I am not sure that buys us much in terms of generalizing the code. Unless I am misunderstanding, that would still leave the impetus of the init/sync/cleanup to the irqfd code, at which point we might as well just leave it entirely in irqfd anyway. Or am I misunderstanding you? > >>>> So while generalizing this perhaps makes sense at some point, >>>> especially >>>> if irqfd-like interfaces get added, it probably doesn't make a ton of >>>> sense to expend energy on it ATM. It is basically a generalization of >>>> the irqfd deferrment code. Lets just wait until we have a user beyond >>>> irqfd for now. Sound acceptable? >>>> >>>> >>> I'll look at v3, but would really like to disentangle this. >>> >> Ok, I will see what I can do. I need at least a v4 to get rid of the >> dependency on the now defunct v3:1/3 patch per yesterdays discussion. >> > > There's another alternative - make ioapic and pic irq-safe by switching > irq locking to spinlocks and using spin_lock_irqsave(). > > I've long opposed this since the ioapic loops on all vcpus when > injecting some irqs and this will increase irqoff times with large > guests. But we don't have large guests now, and we need irq-safe > injection in three places now: > > - irqfd > - pit - we now signal vcpu0 to handle the injection, but this has its > problems > - device assignment > > so it may be better to have irq-safe injection, and deal with the loop > later (would be good to have an idea how exactly). Ok, perhaps I should just hold off on this series for now, then. I can submit the original "assume atomic safe" once the path is fully lockless. -Greg >
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