Re: [PATCH] hw/net: store timers for e1000 in vmstate

[Pavel Dovgalyuk <pavel.dovgalyuk@ispras.ru>]

On 27.10.2021 07:05, Jason Wang wrote:
> On Tue, Oct 26, 2021 at 6:36 PM Pavel Dovgalyuk
> <pavel.dovgalyuk@ispras.ru> wrote:
>>
>> Setting timers randomly when vmstate is loaded breaks
>> execution determinism.
>> Therefore this patch allows saving mit and autoneg timers
>> for e1000. It makes execution deterministic and allows
>> snapshotting and reverse debugging in icount mode.
>>
>> Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgalyuk@ispras.ru>
>> ---
>>   hw/net/e1000.c |   61 ++++++++++++++++++++++++++++++++++++++++++++++----------
>>   1 file changed, 50 insertions(+), 11 deletions(-)
>>
>> diff --git a/hw/net/e1000.c b/hw/net/e1000.c
>> index a30546c5d5..2f706f7298 100644
>> --- a/hw/net/e1000.c
>> +++ b/hw/net/e1000.c
>> @@ -37,6 +37,7 @@
>>   #include "qemu/iov.h"
>>   #include "qemu/module.h"
>>   #include "qemu/range.h"
>> +#include "sysemu/replay.h"
>>
>>   #include "e1000x_common.h"
>>   #include "trace.h"
>> @@ -1407,7 +1408,7 @@ static int e1000_pre_save(void *opaque)
>>        * complete auto-negotiation immediately. This allows us to look
>>        * at MII_SR_AUTONEG_COMPLETE to infer link status on load.
>>        */
>> -    if (nc->link_down && have_autoneg(s)) {
>> +    if (replay_mode == REPLAY_MODE_NONE && nc->link_down && have_autoneg(s)) {
>>           s->phy_reg[PHY_STATUS] |= MII_SR_AUTONEG_COMPLETE;
>>       }
>>
>> @@ -1438,22 +1439,12 @@ static int e1000_post_load(void *opaque, int version_id)
>>               s->mac_reg[TADV] = 0;
>>           s->mit_irq_level = false;
>>       }
>> -    s->mit_ide = 0;
>> -    s->mit_timer_on = true;
>> -    timer_mod(s->mit_timer, qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + 1);
>>
>>       /* nc.link_down can't be migrated, so infer link_down according
>>        * to link status bit in mac_reg[STATUS].
>>        * Alternatively, restart link negotiation if it was in progress. */
>>       nc->link_down = (s->mac_reg[STATUS] & E1000_STATUS_LU) == 0;
>>
>> -    if (have_autoneg(s) &&
>> -        !(s->phy_reg[PHY_STATUS] & MII_SR_AUTONEG_COMPLETE)) {
>> -        nc->link_down = false;
>> -        timer_mod(s->autoneg_timer,
>> -                  qemu_clock_get_ms(QEMU_CLOCK_VIRTUAL) + 500);
>> -    }
> 
> So we won't get those timers armed after migration unconditionally. Is
> this intended?

Not really. I think there could be several solutions:
1. Save some flag to distinguish between old and new state.
2. Use deterministic version for icount (or even record/replay) mode only.
3. Check machine type to change the behavior (as Dave proposed)

> 
> Thanks
> 
>> -
>>       s->tx.props = s->mig_props;
>>       if (!s->received_tx_tso) {
>>           /* We received only one set of offload data (tx.props)
>> @@ -1472,6 +1463,13 @@ static int e1000_tx_tso_post_load(void *opaque, int version_id)
>>       return 0;
>>   }
>>
>> +static int e1000_mit_timer_post_load(void *opaque, int version_id)
>> +{
>> +    E1000State *s = opaque;
>> +    s->mit_timer_on = true;
>> +    return 0;
>> +}
>> +
>>   static bool e1000_mit_state_needed(void *opaque)
>>   {
>>       E1000State *s = opaque;
>> @@ -1493,6 +1491,21 @@ static bool e1000_tso_state_needed(void *opaque)
>>       return chkflag(TSO);
>>   }
>>
>> +static bool e1000_mit_timer_needed(void *opaque)
>> +{
>> +    E1000State *s = opaque;
>> +
>> +    return s->mit_timer_on;
>> +}
>> +
>> +static bool e1000_autoneg_timer_needed(void *opaque)
>> +{
>> +    E1000State *s = opaque;
>> +
>> +    return have_autoneg(s)
>> +           && !(s->phy_reg[PHY_STATUS] & MII_SR_AUTONEG_COMPLETE);
>> +}
>> +
>>   static const VMStateDescription vmstate_e1000_mit_state = {
>>       .name = "e1000/mit_state",
>>       .version_id = 1,
>> @@ -1541,6 +1554,30 @@ static const VMStateDescription vmstate_e1000_tx_tso_state = {
>>       }
>>   };
>>
>> +static const VMStateDescription vmstate_e1000_mit_timer = {
>> +    .name = "e1000/mit_timer",
>> +    .version_id = 1,
>> +    .minimum_version_id = 1,
>> +    .needed = e1000_mit_timer_needed,
>> +    .post_load = e1000_mit_timer_post_load,
>> +    .fields = (VMStateField[]) {
>> +        VMSTATE_TIMER_PTR(mit_timer, E1000State),
>> +        VMSTATE_UINT32(mit_ide, E1000State),
>> +        VMSTATE_END_OF_LIST()
>> +    }
>> +};
>> +
>> +static const VMStateDescription vmstate_e1000_autoneg_timer = {
>> +    .name = "e1000/autoneg_timer",
>> +    .version_id = 1,
>> +    .minimum_version_id = 1,
>> +    .needed = e1000_autoneg_timer_needed,
>> +    .fields = (VMStateField[]) {
>> +        VMSTATE_TIMER_PTR(autoneg_timer, E1000State),
>> +        VMSTATE_END_OF_LIST()
>> +    }
>> +};
>> +
>>   static const VMStateDescription vmstate_e1000 = {
>>       .name = "e1000",
>>       .version_id = 2,
>> @@ -1622,6 +1659,8 @@ static const VMStateDescription vmstate_e1000 = {
>>           &vmstate_e1000_mit_state,
>>           &vmstate_e1000_full_mac_state,
>>           &vmstate_e1000_tx_tso_state,
>> +        &vmstate_e1000_mit_timer,
>> +        &vmstate_e1000_autoneg_timer,
>>           NULL
>>       }
>>   };
>>
>