There are two issues in current code:
1) If the period is changed by re-configuring RegA, the coalesced
irq will be scaled to reflect the new period, however, it
calculates the new interrupt number like this:
s->irq_coalesced = (s->irq_coalesced * s->period) / period;
There are some clocks will be lost if they are not enough to
be squeezed to a single new period that will cause the VM clock
slower
In order to fix the issue, we calculate the interrupt window
based on the precise clock rather than period, then the clocks
lost during period is scaled can be compensated properly
2) If periodic_timer_update() is called due to RegA reconfiguration,
i.e, the period is updated, current time is not the start point
for the next periodic timer, instead, which should start from the
last interrupt, otherwise, the clock in VM will become slow
This patch takes the clocks from last interrupt to current clock
into account and compensates the clocks for the next interrupt,
especially if a complete interrupt was lost in this window, the
time can be caught up by LOST_TICK_POLICY_SLEW
Signed-off-by: Tai Yunfang <yunfangtai@tencent.com>
Signed-off-by: Xiao Guangrong <xiaoguangrong@tencent.com>
Message-Id: <20170510083259.3900-3-xiaoguangrong@tencent.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
369b41359a