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MXS-1948: Do round-robin worker assignment

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Due to the skewed accept distribution without SO_REUSEPORT, we use
round-robin assignment of workers for new client connections. This
provides better performance as work is more likely to be evenly
distributed across all threads.

Using a least-busy-worker algorithm would provide a more stable result but
this is not trivially simple to implement. For this reason, the
round-robin based approach was chosen for 2.2.
This commit is contained in:
Markus Mäkelä
2018-07-02 11:02:04 +03:00
parent e455e7f15d
commit fb1c28c702
3 changed files with 32 additions and 11 deletions
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29
server/core/dcb.cc
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@ -3532,23 +3532,30 @@ int poll_add_dcb(DCB *dcb)
new_state = DCB_STATE_LISTENING;
worker_id = MXS_WORKER_ALL;
}
else if (dcb->dcb_role == DCB_ROLE_CLIENT_HANDLER &&
(strcasecmp(dcb->service->routerModule, "cli") == 0 ||
strcasecmp(dcb->service->routerModule, "maxinfo") == 0))
else if (dcb->dcb_role == DCB_ROLE_CLIENT_HANDLER)
{
// If the DCB refers to an accepted maxadmin/maxinfo socket, we force it
// to the main thread. That's done in order to prevent a deadlock
// that may happen if there are multiple concurrent administrative calls,
// handled by different worker threads.
// See: https://jira.mariadb.org/browse/MXS-1805 and https://jira.mariadb.org/browse/MXS-1833
if (strcasecmp(dcb->service->routerModule, "cli") == 0 ||
strcasecmp(dcb->service->routerModule, "maxinfo") == 0)
{
// If the DCB refers to an accepted maxadmin/maxinfo socket, we force it
// to the main thread. That's done in order to prevent a deadlock
// that may happen if there are multiple concurrent administrative calls,
// handled by different worker threads.
// See: https://jira.mariadb.org/browse/MXS-1805 and https://jira.mariadb.org/browse/MXS-1833
dcb->poll.thread.id = 0;
}
else
{
// Round-robin the client connection worker assignment
dcb->poll.thread.id = Worker::pick_worker_id();
}
new_state = DCB_STATE_POLLING;
dcb->poll.thread.id = 0;
worker_id = dcb->poll.thread.id;
}
else
{
ss_dassert(dcb->dcb_role == DCB_ROLE_CLIENT_HANDLER ||
dcb->dcb_role == DCB_ROLE_BACKEND_HANDLER);
ss_dassert(dcb->dcb_role == DCB_ROLE_BACKEND_HANDLER);
ss_dassert(Worker::get_current_id() != -1);
ss_dassert(Worker::get_current_id() == dcb->poll.thread.id);