Messages in this thread | | | Subject | Re: [4.2] commit d59cfc09c32 (sched, cgroup: replace signal_struct->group_rwsem with a global percpu_rwsem) causes regression for libvirt/kvm | From | Christian Borntraeger <> | Date | Wed, 16 Sep 2015 13:50:28 +0200 |
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Am 16.09.2015 um 13:03 schrieb Tejun Heo: > Hello, > > On Wed, Sep 16, 2015 at 12:58:00PM +0200, Christian Borntraeger wrote: >> FWIW, I added a printk to percpu_down_write. With KVM and uprobes disabled, >> just booting up a fedora20 gives me __6749__ percpu_down_write calls on 4.2. >> systemd seems to do that for the processes. >> >> So a revert is really the right thing to do. In fact, I dont know if the >> rcu_sync_enter rework is enough. With systemd setting the cgroup seem to >> be NOT a cold/seldom case. > > Booting would usually be the hottest operation for that and it's still > *relatively* cold path compared to the reader side which is task > fork/exit paths. The whole point is shift overhead from hotter reader > side. Can you see problems with percpu_rwsem rework?
As I said, it seems the rcu tree with that change seems to work fine on my system. This needs a more testing on other machines, though. I guess a revert plus a re-add in the 4.4 merge window should give us enough test coverage.
Christian
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