* zhanghailiang (zhang.zhanghailiang@xxxxxxxxxx) wrote: > On 2015/5/29 9:29, Wen Congyang wrote: > >On 05/29/2015 12:24 AM, Dr. David Alan Gilbert wrote: > >>* zhanghailiang (zhang.zhanghailiang@xxxxxxxxxx) wrote: > >>>This is the 5th version of COLO, here is only COLO frame part, include: VM checkpoint, > >>>failover, proxy API, block replication API, not include block replication. > >>>The block part has been sent by wencongyang: > >>>"[Qemu-devel] [PATCH COLO-Block v5 00/15] Block replication for continuous checkpoints" > >>> > >>>we have finished some new features and optimization on COLO (As a development branch in github), > >>>but for easy of review, it is better to keep it simple now, so we will not add too much new > >>>codes into this frame patch set before it been totally reviewed. > >>> > >>>You can get the latest integrated qemu colo patches from github (Include Block part): > >>>https://github.com/coloft/qemu/commits/colo-v1.2-basic > >>>https://github.com/coloft/qemu/commits/colo-v1.2-developing (more features) > >>> > >>>Please NOTE the difference between these two branch. > >>>colo-v1.2-basic is exactly same with this patch series, which has basic features of COLO. > >>>Compared with colo-v1.2-basic, colo-v1.2-developing has some optimization in the > >>>process of checkpoint, including: > >>> 1) separate ram and device save/load process to reduce size of extra memory > >>> used during checkpoint > >>> 2) live migrate part of dirty pages to slave during sleep time. > >>>Besides, we add some statistic info in colo-v1.2-developing, which you can get these stat > >>>info by using command 'info migrate'. > >> > >> > >>Hi, > >> I have that running now. > >> > >>Some notes: > >> 1) The colo-proxy is working OK until qemu quits, and then it gets an RCU problem; see below > >> 2) I've attached some minor tweaks that were needed to build with the 4.1rc kernel I'm using; > >> they're very minor changes and I don't think related to (1). > >> 3) I've also included some minor fixups I needed to get the -developing world > >> to build; my compiler is fussy about unused variables etc - but I think the code > >> in ram_save_complete in your -developing patch is wrong because there are two > >> 'pages' variables and the one in the inner loop is the only one changed. > > Oops, i will fix them. thank you for pointing out this low grade mistake. :) No problem; we all make them. > >> 4) I've started trying simple benchmarks and tests now: > >> a) With a simple web server most requests have very little overhead, the comparison > >> matches most of the time; I do get quite large spikes (0.04s->1.05s) which I guess > >> corresponds to when a checkpoint happens, but I'm not sure why the spike is so big, > >> since the downtime isn't that big. > > Have you disabled DEBUG for colo proxy? I turned it on in default, is this related? Yes, I've turned that off, I still get the big spikes; not looked why yet. > >> b) I tried something with more dynamic pages - the front page of a simple bugzilla > >> install; it failed the comparison every time; it took me a while to figure out > > Failed comprison ? Do you mean the net packets in these two sides are always inconsistent? Yes. > >> why, but it generates a unique token in it's javascript each time (for a password reset > >> link), and I guess the randomness used by that doesn't match on the two hosts. > >> It surprised me, because I didn't expect this page to have much randomness > >> in. > >> > >> 4a is really nice - it shows the benefit of COLO over the simple checkpointing; > >>checkpoints happen very rarely. > >> > >>The colo-proxy rcu problem I hit shows as rcu-stalls in both primary and secondary > >>after the qemu quits; the backtrace of the qemu stack is: > > > >How to reproduce it? Use monitor command quit to quit qemu? Or kill the qemu? > > > >> > >>[<ffffffff810d8c0c>] wait_rcu_gp+0x5c/0x80 > >>[<ffffffff810ddb05>] synchronize_rcu+0x45/0xd0 > >>[<ffffffffa0a251e5>] colo_node_release+0x35/0x50 [nfnetlink_colo] > >>[<ffffffffa0a25795>] colonl_close_event+0xe5/0x160 [nfnetlink_colo] > >>[<ffffffff81090c96>] notifier_call_chain+0x66/0x90 > >>[<ffffffff8109154c>] atomic_notifier_call_chain+0x6c/0x110 > >>[<ffffffff815eee07>] netlink_release+0x5b7/0x7f0 > >>[<ffffffff815878bf>] sock_release+0x1f/0x90 > >>[<ffffffff81587942>] sock_close+0x12/0x20 > >>[<ffffffff812193c3>] __fput+0xd3/0x210 > >>[<ffffffff8121954e>] ____fput+0xe/0x10 > >>[<ffffffff8108d9f7>] task_work_run+0xb7/0xf0 > >>[<ffffffff81002d4d>] do_notify_resume+0x8d/0xa0 > >>[<ffffffff81722b66>] int_signal+0x12/0x17 > >>[<ffffffffffffffff>] 0xffffffffffffffff > > > >Thanks for your test. The backtrace is very useful, and we will fix it soon. > > > > Yes, it is a bug, the callback function colonl_close_event() is called when holding > rcu lock: > netlink_release > ->atomic_notifier_call_chain > ->rcu_read_lock(); > ->notifier_call_chain > ->ret = nb->notifier_call(nb, val, v); > And here it is wrong to call synchronize_rcu which will lead to sleep. > Besides, there is another function might lead to sleep, kthread_stop which is called > in destroy_notify_cb. > > >> > >>that's with both the 423a8e268acbe3e644a16c15bc79603cfe9eb084 from yesterday and > >>older e58e5152b74945871b00a88164901c0d46e6365e tags on colo-proxy. > >>I'm not sure of the right fix; perhaps it might be possible to replace the > >>synchronize_rcu in colo_node_release by a call_rcu that does the kfree later? > > > >I agree with it. > > That is a good solution, i will fix both of the above problems. Thanks, Dave > > Thanks, > zhanghailiang > > > > >> > >>Thanks, > >> > >>Dave > >> > >>> > > > > > >. > > > > -- Dr. David Alan Gilbert / dgilbert@xxxxxxxxxx / Manchester, UK -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
