Raghavendra Gowdappa wrote: > > > ----- 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. > Just fyi, I did have a loop on the read() code. Past experience is that a write() only fails when the pipe is full and, as someone else noted, that should have triggered the poll(). I did have log message stuff in the code I was testing, but I didn't look at it closely once I saw it was broken. I just went back to what worked. I may test this some more someday, but until then, the code in 3.7.6 works ok. Thanks for your comments, rick > > > > 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
