[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] Proposed new "memory capacity claim" hypercall/feature
>>> On 08.11.12 at 10:12, Keir Fraser <keir@xxxxxxx> wrote: > On 08/11/2012 08:54, "Jan Beulich" <JBeulich@xxxxxxxx> wrote: >> That may have mattered when ioctl-s were run with the big kernel >> lock held, but even 2.6.18 didn't do that anymore (using the >> .unlocked_ioctl field of struct file_operations), which means >> that even softirqs will get serviced in Dom0 since the preempted >> hypercall gets restarted via exiting to the guest (i.e. events get >> delivered). Scheduling is what indeed wouldn't happen, but if >> allocation latency can be brought down, 8M might turn out pretty >> small a chunk size. > > Ah, then I am out of date on how Linux services softirqs and preemption? Can > softirqs/preemption occur any time, even in kernel mode, so long as no locks > are held? > > I thought softirq-type work only happened during event servicing, only if > the event servicing had interrupted user context (ie, would not happen if > started from within kernel mode). So the restart of the hypercall trap > instruction would be an opportunity to service hardirqs, but not softirqs or > scheduler... No, irq_exit() can invoke softirqs, provided this isn't a nested IRQ (soft as well as hard) or softirqs weren't disabled in the interrupted context. The only thing that indeed is - on non-preemptible kernels - done only on exit to user mode is the eventual entering of the scheduler. Jan _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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