On Sat, 2015-11-21 at 13:56 +0100, Paolo Bonzini wrote:
>
> 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.
I found it.
diff --git a/hw/block/nvme.c b/hw/block/nvme.c
index 31572f2..f27fd35 100644
--- a/hw/block/nvme.c
+++ b/hw/block/nvme.c
@@ -548,6 +548,7 @@ static void nvme_cq_notifier(EventNotifier *e)
NvmeCQueue *cq =
container_of(e, NvmeCQueue, notifier);
+ event_notifier_test_and_clear(&cq->notifier);
nvme_post_cqes(cq);
}
@@ -567,6 +568,7 @@ static void nvme_sq_notifier(EventNotifier *e)
NvmeSQueue *sq =
container_of(e, NvmeSQueue, notifier);
+ event_notifier_test_and_clear(&sq->notifier);
nvme_process_sq(sq);
}
Here is new performance number:
qemu-nvme + google-ext + eventfd: 294MB/s
virtio-blk: 344MB/s
virtio-scsi: 296MB/s
It's almost same as virtio-scsi. Nice.
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