On 10/15/2010 03:52 AM, Ian Campbell wrote:
> This ensures that system is updated before calling any hard irq
> handlers after a long period of ticklessness. If we do not do this
> then hardirq will see a jiffies from before the period of ticklessness
> and make intcorrect decisions regarding timer expiry etc.
>
> This resolves issues e.g. with USB keyboard timer repeats.
>
> Based on a patch by Keir Fraser.
I talked about this with James, and it makes no sense to me at all.
J
> Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
> Cc: keir@xxxxxxx
> ---
> drivers/xen/events.c | 22 +++++++++++++++++++++-
> 1 files changed, 21 insertions(+), 1 deletions(-)
>
> diff --git a/drivers/xen/events.c b/drivers/xen/events.c
> index c9d1d4a..1496ba5 100644
> --- a/drivers/xen/events.c
> +++ b/drivers/xen/events.c
> @@ -1052,6 +1052,7 @@ static void __xen_evtchn_do_upcall(struct pt_regs *regs)
>
> do {
> unsigned long pending_words;
> + int irq;
>
> vcpu_info->evtchn_upcall_pending = 0;
>
> @@ -1062,6 +1063,24 @@ static void __xen_evtchn_do_upcall(struct pt_regs
> *regs)
> /* Clear master flag /before/ clearing selector flag. */
> wmb();
> #endif
> +
> + /*
> + * Handle timer interrupts before all others, so that all
> + * hardirq handlers see an up-to-date system time even if we
> + * have just woken from a long idle period.
> + */
> + irq = percpu_read(virq_to_irq[VIRQ_TIMER]);
> + if (irq != -1) {
> + int word_idx;
> + int bit_idx;
> + int port = evtchn_from_irq(irq);
> + word_idx = port / BITS_PER_LONG;
> + bit_idx = port % BITS_PER_LONG;
> + if (VALID_EVTCHN(port) &&
> + (active_evtchns(cpu, s, word_idx) & (1UL<<bit_idx)))
> + (void)handle_irq(irq, regs);
> + }
> +
> pending_words = xchg(&vcpu_info->evtchn_pending_sel, 0);
> while (pending_words != 0) {
> unsigned long pending_bits;
> @@ -1071,9 +1090,10 @@ static void __xen_evtchn_do_upcall(struct pt_regs
> *regs)
> while ((pending_bits = active_evtchns(cpu, s,
> word_idx)) != 0) {
> int bit_idx = __ffs(pending_bits);
> int port = (word_idx * BITS_PER_LONG) + bit_idx;
> - int irq = evtchn_to_irq[port];
> struct irq_desc *desc;
>
> + irq = evtchn_to_irq[port];
> +
> mask_evtchn(port);
> clear_evtchn(port);
>
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