Hi Ben, Do you mean that there some threads in in ovsrcu_threads list were wrongly using seq_wait or rcu functions?
Thanks, I will do some more research on this problem. > -----Original Message----- > From: Ben Pfaff [mailto:[email protected]] > Sent: Monday, December 10, 2018 10:08 AM > To: Lilijun (Jerry, Cloud Networking) <[email protected]> > Cc: [email protected] > Subject: Re: [ovs-dev] [PATCH] [PATCH] rcu: reduce RCU block time > > If that's the case, then there's something wrong with seq_wait() or the use > of it in this context. The timer logic here is just to issue log messages. > > It would be better to figure out the real problem, because that would reduce > the 100 ms (or 1000 ms) latency to near-zero. > > On Mon, Dec 10, 2018 at 01:50:41AM +0000, Lilijun (Jerry, Cloud Networking) > wrote: > > Hi, Ben > > > > Thanks for your reply. > > > > Do you mean that the function poll_timer_wait_until(start + > warning_threshold) call only wakeup to do some need log messages and > ovsrcu_synchronize() will wait for seq_wait()? > > > > According to my understanding, ovsrcu_synchronize() will return until > every thread in ovsrcu_threads list have change their seqno to target_seqno. > When some thread call ovsrcu_quiesce(), global_seqno is changed. Then > seq_wait() will check if global_seqno is changed and call > poll_immediate_wake_at() to finish the poll_block()'s waiting. > > > > We assume that the first call of seq_wait() in this loop check global_seqno > failed for other thread hasn't been ready to call ovsrcu_quiesce(). Then the > loop will sleep 1000ms(set by warning_threshold) by poll_block() and check > the thread's seqno or global_seqno again when no other threads finish the > poll_block()'s waiting in early. > > > > If we set warning_threshold to 100ms, the look will check the seqno more > frequently and may break earlier. I have test it myself, when > warning_threshold is set to 100 as default, the loop 's time indeed reduce to > 100ms, that's maybe some evidence. > > > > > > > > > -----Original Message----- > > > From: Ben Pfaff [mailto:[email protected]] > > > Sent: Friday, December 07, 2018 10:37 PM > > > To: Lilijun (Jerry, Cloud Networking) <[email protected]> > > > Cc: [email protected] > > > Subject: Re: [ovs-dev] [PATCH] [PATCH] rcu: reduce RCU block time > > > > > > On Fri, Dec 07, 2018 at 02:03:27PM +0800, Lilijun wrote: > > > > When calling ovsrcu_synchronize(), it always block 1000ms because > > > > we poll block until elapsed time become greater than > > > > warning_threshold(1000).That's too long for some configuration > commands. > > > > So this patch reduces warning_threshold's default value to 100 and > > > > print logs after it have elapsed more than 1000ms. > > > > > > > > Signed-off-by: Lilijun <[email protected]> > > > > > > This only makes any sense if the seq_wait() doesn't work. Do you > > > have evidence that is the case? _______________________________________________ dev mailing list [email protected] https://mail.openvswitch.org/mailman/listinfo/ovs-dev
