Vivek Goyal wrote: > On Tue, Jul 28, 2009 at 01:44:32PM +0200, Jerome Marchand wrote: >> Vivek Goyal wrote: >>> Hi Jerome, >>> >>> Thanks for testing it out. I could also reproduce the issue. >>> >>> I had assumed that RT queue will always preempt non-RT queue and hence if >>> there is an RT ioq/request pending, the sd->next_entity will point to >>> itself and any queue which is preempting it has to be on same service >>> tree. >>> >>> But in your test case it looks like that RT async queue is pending and >>> there is some sync BE class IO going on. It looks like that CFQ allows >>> sync queue preempting async queue irrespective of class, so in this case >>> sync BE class reader will preempt async RT queue and that's where my >>> assumption is broken and we see BUG_ON() hitting. >>> >>> Can you please tryout following patch. It is a quick patch and requires >>> more testing. It solves the crash but still does not solve the issue of >>> sync queue always preempting async queues irrespective of class. In >>> current scheduler we always schedule the RT queue first (whether it be >>> sync or async). This problem requires little more thought. >> I've tried it: I can't reproduce the issue anymore and I haven't seen any >> other problem so far. >> By the way, what is the expected result regarding fairness among different >> groups when IO from different classes are run on each group? For instance, >> if we have RT IO going on on one group, BE IO on an other and Idle IO on a >> third group, what is the expected result: should the IO time been shared >> fairly between the groups or should RT IO have priority? As it is now, the >> time is shared fairly between BE and RT groups and the last group running >> Idle IO hardly get any time. >> > > Hi Jerome, > > If there are two groups RT and BE, I would expect RT group to get all the > bandwidth as long as it is backlogged and starve the BE group. I wasn't clear enough. I meant the class of the process as set by ionice, not the class of the cgroup. That is, of course, only an issue when using CFQ. > > I ran quick test of two dd readers. One reader is in RT group and other is > in BE group. I do see that RT group runs away with almost all the BW. > > group1 time=8:16 2479 group1 sectors=8:16 457848 > group2 time=8:16 103 group2 sectors=8:16 18936 > > Note that when group1 (RT) finished it had got 2479 ms of disk time while > group2 (BE) got only 103 ms. > > Can you send details of your test. It should not be fair sharing between > RT and BE group. Setup: $ mount -t cgroup -o io,blkio none /cgroup $ mkdir /cgroup/test1 /cgroup/test2 /cgroup/test3 $ echo 1000 > /cgroup/test1/io.weight $ echo 1000 > /cgroup/test2/io.weight $ echo 1000 > /cgroup/test3/io.weight Test: $ echo 3 > /proc/sys/vm/drop_caches $ ionice -c 1 dd if=/tmp/io-controller-test3 of=/dev/null & $ echo $! > /cgroup/test1/tasks $ ionice -c 2 dd if=/tmp/io-controller-test1 of=/dev/null & $ echo $! > /cgroup/test2/tasks $ ionice -c 3 dd if=/tmp/io-controller-test2 of=/dev/null & $ echo $! > /cgroup/test3/tasks > > Thanks > Vivek Jerome _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers
