Reading data before peered to improve performance

["xsong682@xxxxxxxx" <xsong682@xxxxxxxx>]

In current code, before PG peered, PG can’t do any operations including reading in following code

void PrimaryLogPG::do_request( OpRequestRef& op, ThreadPool::TPHandle &handle)
{

if (!is_peered()) {
// Delay unless PGBackend says it's ok
if (pgbackend->can_handle_while_inactive(op)) {
bool handled = pgbackend->handle_message(op);
assert(handled);
return;
} else {
waiting_for_peered.push_back(op);
op->mark_delayed("waiting for peered");
return;
}
}

that will impact performance, I think the primary OSD control the data writing, if it haven’t got changed, the data on the primary OSD is always correct except silent data error, so the data can be read safely before peered. 
If it's ok, another question is how to know the OSD haven’t changed? Checking “primary of acting_set == primary of up_set” is enough or not? Should we check interval for the situation primary OSD change from “A-->B-->A”?

Thanks,
Xiaobing


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