On 21/11/2015 00:05, Ming Lin wrote:

[    1.752129] Freeing unused kernel memory: 420K (ffff880001b97000 - ffff880001c00000)
[    1.986573] clocksource: tsc: mask: 0xffffffffffffffff max_cycles: 0x30e5c9bbf83, max_idle_ns: 440795378954 ns
[    1.988187] clocksource: Switched to clocksource tsc
[    3.235423] clocksource: timekeeping watchdog: Marking clocksource 'tsc' as unstable because the skew is too large:
[    3.358713] clocksource:                       'refined-jiffies' wd_now: fffeddf3 wd_last: fffedd76 mask: ffffffff
[    3.410013] clocksource:                       'tsc' cs_now: 3c121d4ec cs_last: 340888eb7 mask: ffffffffffffffff
[    3.450026] clocksource: Switched to clocksource refined-jiffies
[    7.696769] Adding 392188k swap on /dev/vda5.  Priority:-1 extents:1 across:392188k 
[    7.902174] EXT4-fs (vda1): re-mounted. Opts: (null)
[    8.734178] EXT4-fs (vda1): re-mounted. Opts: errors=remount-ro

Then it doesn't response input for almost 1 minute.
Without this patch, kernel loads quickly.

Interesting.  I guess there's time to debug it, since QEMU 2.6 is still 
a few months away.  In the meanwhile we can apply your patch as is, 
apart from disabling the "if (new_head >= cq->size)" and the similar 
one for "if (new_ tail >= sq->size".

But, I have a possible culprit.  In your nvme_cq_notifier you are not doing the 
equivalent of:

	start_sqs = nvme_cq_full(cq) ? 1 : 0;
        cq->head = new_head;
        if (start_sqs) {
            NvmeSQueue *sq;
            QTAILQ_FOREACH(sq, &cq->sq_list, entry) {
                timer_mod(sq->timer, qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + 500);
            }
            timer_mod(cq->timer, qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + 500);
        }

Instead, you are just calling nvme_post_cqes, which is the equivalent of

	timer_mod(cq->timer, qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + 500);

Adding a loop to nvme_cq_notifier, and having it call nvme_process_sq, might
fix the weird 1-minute delay.

Paolo

void memory_region_add_eventfd(MemoryRegion *mr,
                               hwaddr addr,
                               unsigned size,
                               bool match_data,
                               uint64_t data,
                               EventNotifier *e)

Could you help to explain what "match_data" and "data" mean?

If match_data is true, the eventfd is only signalled if "data" is being written to memory.

Paolo