2011/1/4 Michael S. Tsirkin <mst@xxxxxxxxxx>:
> On Tue, Jan 04, 2011 at 09:20:53PM +0900, Yoshiaki Tamura wrote:
>> 2011/1/4 Michael S. Tsirkin <mst@xxxxxxxxxx>:
>> > On Tue, Jan 04, 2011 at 08:02:54PM +0900, Yoshiaki Tamura wrote:
>> >> 2010/11/29 Stefan Hajnoczi <stefanha@xxxxxxxxx>:
>> >> > On Thu, Nov 25, 2010 at 6:06 AM, Yoshiaki Tamura
>> >> > <tamura.yoshiaki@xxxxxxxxxxxxx> wrote:
>> >> >> event-tap controls when to start FT transaction, and provides proxy
>> >> >> functions to called from net/block devices. While FT transaction, it
>> >> >> queues up net/block requests, and flush them when the transaction gets
>> >> >> completed.
>> >> >>
>> >> >> Signed-off-by: Yoshiaki Tamura <tamura.yoshiaki@xxxxxxxxxxxxx>
>> >> >> Signed-off-by: OHMURA Kei <ohmura.kei@xxxxxxxxxxxxx>
>> >> >> ---
>> >> >> Makefile.target | 1 +
>> >> >> block.h | 9 +
>> >> >> event-tap.c | 794 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
>> >> >> event-tap.h | 34 +++
>> >> >> net.h | 4 +
>> >> >> net/queue.c | 1 +
>> >> >> 6 files changed, 843 insertions(+), 0 deletions(-)
>> >> >> create mode 100644 event-tap.c
>> >> >> create mode 100644 event-tap.h
>> >> >
>> >> > event_tap_state is checked at the beginning of several functions. If
>> >> > there is an unexpected state the function silently returns. Should
>> >> > these checks really be assert() so there is an abort and backtrace if
>> >> > the program ever reaches this state?
>> >> >
>> >> >> +typedef struct EventTapBlkReq {
>> >> >> + char *device_name;
>> >> >> + int num_reqs;
>> >> >> + int num_cbs;
>> >> >> + bool is_multiwrite;
>> >> >
>> >> > Is multiwrite logging necessary? If event tap is called from within
>> >> > the block layer then multiwrite is turned into one or more
>> >> > bdrv_aio_writev() calls.
>> >> >
>> >> >> +static void event_tap_replay(void *opaque, int running, int reason)
>> >> >> +{
>> >> >> + EventTapLog *log, *next;
>> >> >> +
>> >> >> + if (!running) {
>> >> >> + return;
>> >> >> + }
>> >> >> +
>> >> >> + if (event_tap_state != EVENT_TAP_LOAD) {
>> >> >> + return;
>> >> >> + }
>> >> >> +
>> >> >> + event_tap_state = EVENT_TAP_REPLAY;
>> >> >> +
>> >> >> + QTAILQ_FOREACH(log, &event_list, node) {
>> >> >> + EventTapBlkReq *blk_req;
>> >> >> +
>> >> >> + /* event resume */
>> >> >> + switch (log->mode & ~EVENT_TAP_TYPE_MASK) {
>> >> >> + case EVENT_TAP_NET:
>> >> >> + event_tap_net_flush(&log->net_req);
>> >> >> + break;
>> >> >> + case EVENT_TAP_BLK:
>> >> >> + blk_req = &log->blk_req;
>> >> >> + if ((log->mode & EVENT_TAP_TYPE_MASK) == EVENT_TAP_IOPORT) {
>> >> >> + switch (log->ioport.index) {
>> >> >> + case 0:
>> >> >> + cpu_outb(log->ioport.address, log->ioport.data);
>> >> >> + break;
>> >> >> + case 1:
>> >> >> + cpu_outw(log->ioport.address, log->ioport.data);
>> >> >> + break;
>> >> >> + case 2:
>> >> >> + cpu_outl(log->ioport.address, log->ioport.data);
>> >> >> + break;
>> >> >> + }
>> >> >> + } else {
>> >> >> + /* EVENT_TAP_MMIO */
>> >> >> + cpu_physical_memory_rw(log->mmio.address,
>> >> >> + log->mmio.buf,
>> >> >> + log->mmio.len, 1);
>> >> >> + }
>> >> >> + break;
>> >> >
>> >> > Why are net tx packets replayed at the net level but blk requests are
>> >> > replayed at the pio/mmio level?
>> >> >
>> >> > I expected everything to replay either as pio/mmio or as net/block.
>> >>
>> >> Stefan,
>> >>
>> >> After doing some heavy load tests, I realized that we have to
>> >> take a hybrid approach to replay for now. This is because when a
>> >> device moves to the next state (e.g. virtio decreases inuse) is
>> >> different between net and block. For example, virtio-net
>> >> decreases inuse upon returning from the net layer,
>> >> but virtio-blk
>> >> does that inside of the callback.
>> >
>> > For TX, virtio-net calls virtqueue_push from virtio_net_tx_complete.
>> > For RX, virtio-net calls virtqueue_flush from virtio_net_receive.
>> > Both are invoked from a callback.
>> >
>> >> If we only use pio/mmio
>> >> replay, even though event-tap tries to replay net requests, some
>> >> get lost because the state has proceeded already.
>> >
>> > It seems that all you need to do to avoid this is to
>> > delay the callback?
>>
>> Yeah, if it's possible. But if you take a look at virtio-net,
>> you'll see that virtio_push is called immediately after calling
>> qemu_sendv_packet
>> while virtio-blk does that in the callback.
>
> This is only if the packet was sent immediately.
> I was referring to the case where the packet is queued.
I see. I usually don't see packets get queued in the net layer.
What would be the effect to devices? Restraint sending packets?
>
>> >
>> >> This doesn't
>> >> happen with block, because the state is still old enough to
>> >> replay. Note that using hybrid approach won't cause duplicated
>> >> requests on the secondary.
>> >
>> > An assumption devices make is that a buffer is unused once
>> > completion callback was invoked. Does this violate that assumption?
>>
>> No, it shouldn't. In case of net with net layer replay, we copy
>> the content of the requests, and in case of block, because we
>> haven't called the callback yet, the requests remains fresh.
>>
>> Yoshi
>>
>
> Yes, as long as you copy it should be fine. Maybe it's a good idea for
> event-tap to queue all packets to avoid the copy and avoid the need to
> replay at the net level.
If queuing works fine for the devices, it seems to be a good
idea. I think the ordering issue doesn't happen still.
Yoshi
>
>> >
>> > --
>> > MST
>> >
>> >
>
>
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