----- Original Message ----- > From: "Rick Macklem" <rmacklem@xxxxxxxxxxx> > To: "Raghavendra Gowdappa" <rgowdapp@xxxxxxxxxx> > Cc: "Jeff Darcy" <jdarcy@xxxxxxxxxx>, "Raghavendra G" <raghavendra@xxxxxxxxxxx>, "freebsd-fs" > <freebsd-fs@xxxxxxxxxxx>, "Hubbard Jordan" <jkh@xxxxxxxxxxxxx>, "Xavier Hernandez" <xhernandez@xxxxxxxxxx>, "Gluster > Devel" <gluster-devel@xxxxxxxxxxx> > Sent: Tuesday, January 19, 2016 4:07:09 AM > Subject: Re: FreeBSD port of GlusterFS racks up a lot of CPU usage > > Raghavendra Gowdappa wrote: > > > > > > ----- Original Message ----- > > > From: "Rick Macklem" <rmacklem@xxxxxxxxxxx> > > > To: "Jeff Darcy" <jdarcy@xxxxxxxxxx> > > > Cc: "Raghavendra G" <raghavendra@xxxxxxxxxxx>, "freebsd-fs" > > > <freebsd-fs@xxxxxxxxxxx>, "Hubbard Jordan" > > > <jkh@xxxxxxxxxxxxx>, "Xavier Hernandez" <xhernandez@xxxxxxxxxx>, "Gluster > > > Devel" <gluster-devel@xxxxxxxxxxx> > > > Sent: Saturday, January 9, 2016 7:29:59 AM > > > Subject: Re: FreeBSD port of GlusterFS racks up a lot of > > > CPU usage > > > > > > Jeff Darcy wrote: > > > > > > I don't know anything about gluster's poll implementation so I may > > > > > > be totally wrong, but would it be possible to use an eventfd (or a > > > > > > pipe if eventfd is not supported) to signal the need to add more > > > > > > file descriptors to the poll call ? > > > > > > > > > > > > > > > > > > The poll call should listen on this new fd. When we need to change > > > > > > the fd list, we should simply write to the eventfd or pipe from > > > > > > another thread. This will cause the poll call to return and we > > > > > > will > > > > > > be able to change the fd list without having a short timeout nor > > > > > > having to decide on any trade-off. > > > > > > > > > > > > > > > Thats a nice idea. Based on my understanding of why timeouts are > > > > > being > > > > > used, this approach can work. > > > > > > > > The own-thread code which preceded the current poll implementation did > > > > something similar, using a pipe fd to be woken up for new *outgoing* > > > > messages. That code still exists, and might provide some insight into > > > > how to do this for the current poll code. > > > I took a look at event-poll.c and found something interesting... > > > - A pipe called "breaker" is already set up by event_pool_new_poll() and > > > closed by event_pool_destroy_poll(), however it never gets used for > > > anything. > > > > I did a check on history, but couldn't find any information on why it was > > removed. Can you send this patch to http://review.gluster.org ? We can > > review and merge the patch over there. If you are not aware, development > > work flow can be found at: > > > > http://www.gluster.org/community/documentation/index.php/Developers > > > Actually, the patch turned out to be a flop. Sometimes a fuse mount would end > up with an empty file system with the patch. (I don't know why it was broken, > but maybe the original author tan into issues as well?) +static void +event_pool_changed (struct event_pool *event_pool) +{ + + /* Write a byte into the breaker pipe to wake up poll(). */ + if (event_pool->breaker[1] >= 0) + write(event_pool->breaker[1], "X", 1); +} breaker is set to non-blocking on both read and write ends. So, probably write might be failing sometimes with EAGAIN/EBUSY and thereby preventing the socket from being registered. Probably that might be the reason? if (event_pool->breaker[1] >= 0) { do { ret = write(event_pool->breaker[1], "X", 1); } while (ret != 1); } Also similar logic might be required while flushing out junk from read end too. > > Anyhow, I am now using the 3.7.6 event-poll.c code except that I have > increased > the timeout from 1msec->10msec. (Going from 1->5->10 didn't seem to cause a > problem, but I got slower test runs when I increased to 20msec, so I've > settled on > 10mses. This does reduce the CPU usage when the GlusterFS file systems aren't > active.) > I will submit this one line change to your workflow if it continues to test > ok. > > Thanks for everyone's input, rick > > > > > > > So, I added a few lines of code that writes a byte to it whenever the > > > list > > > of > > > file descriptors is changed and read when poll() returns, if its revents > > > is > > > set. > > > I also changed the timeout to -1 (infinity) and it seems to work for a > > > trivial > > > test. > > > --> Btw, I also noticed the "changed" variable gets set to 1 on a change, > > > but > > > never reset to 0. I didn't change this, since it looks "racey". (ie. > > > I > > > think you could easily get a race between a thread that clears it and > > > one > > > that adds a new fd.) > > > > > > A slightly safer version of the patch would set a long (100msec ??) > > > timeout > > > instead > > > of -1. > > > > > > Anyhow, I've attached the patch in case anyone would like to try it and > > > will > > > create a bug report for this after I've had more time to test it. > > > (I only use a couple of laptops, so my testing will be minimal.) > > > > > > Thanks for all the help, rick > > > > > > > _______________________________________________ > > > > freebsd-fs@xxxxxxxxxxx mailing list > > > > https://lists.freebsd.org/mailman/listinfo/freebsd-fs > > > > To unsubscribe, send any mail to "freebsd-fs-unsubscribe@xxxxxxxxxxx" > > > > > > > > > > _______________________________________________ Gluster-devel mailing list Gluster-devel@xxxxxxxxxxx http://www.gluster.org/mailman/listinfo/gluster-devel
