On 09/21/2017 11:15 AM, Cornelia Huck wrote:
>> +static inline CcwDataStream *get_cds(Terminal3270 *t)
>> +{
>> + return &(CCW_DEVICE(&t->cdev)->sch->cds);
>> +}
>> +
>> +static int read_payload_3270(EmulatedCcw3270Device *dev)
>> {
>> Terminal3270 *t = TERMINAL_3270(dev);
>> int len;
>>
>> - len = MIN(count, t->in_len);
>> - cpu_physical_memory_write(cda, t->inv, len);
>> + len = MIN(ccw_dstream_avail(get_cds(t)), t->in_len);
>> + ccw_dstream_write_buf(get_cds(t), t->inv, len);
> CCW_DEVICE() as called by get_cds() goes through qom, which implies a
> bit of overhead. Not sure if it makes sense to cache it in this
> function so you don't go through it multiple times. (Dito for the other
> callback.)
>
I've cargo-culted this way of getting CCW_DEVICE(&t->cdev) to the CcwDevice
form terminal_read (the pattern used at multiple places in the file). As
far as I can tell, the overhead basically depends on CONFIG_QOM_CAST_DEBUG.
I have no idea what do we have in production, but my guess is, that
ONFIG_QOM_CAST_DEBUG makes only sense for development and testing
(especially if proper test coverage is assumed).
Can you enlighten me?
CCW_DEVICE() may contain a run-time check (depending on CONFIG_QOM_CAST_DEBUG),
we however can make sure things are OK at compile time. This brings
me to the next question. Does it even make sense to use OBJECT_CHECK based
constructs when going from specific to general (we don't actually need a
cast here)? Obviously, for the other direction we really need a cast, so doing
a run-time check there does indeed provide added value.
Halil
>> t->in_len -= len;
>>
>> return len;
