On 11/23/2010 05:43 PM, Colin Cross wrote: > synchronize_rcu can be very expensive, averaging 100 ms in > some cases. In cgroup_attach_task, it is used to prevent > a task->cgroups pointer dereferenced in an RCU read side > critical section from being invalidated by delaying the call > to put_css_set until after an RCU grace period. > > To avoid the call to synchronize_rcu, make the put_css_set > call rcu-safe by moving the deletion of the css_set links > into rcu-protected free_css_set_rcu. > > The calls to check_for_release in free_css_set_rcu now occur > in softirq context, so convert all uses of the > release_list_lock spinlock to irq safe versions. > > The decrement of the cgroup refcount is no longer > synchronous with the call to put_css_set, which can result > in the cgroup refcount staying positive after the last call > to cgroup_attach_task returns. To allow the cgroup to be > deleted with cgroup_rmdir synchronously after > cgroup_attach_task, introduce a second refcount, > rmdir_count, that is decremented synchronously in > put_css_set. If cgroup_rmdir is called on a cgroup for > hich rmdir_count is zero but count is nonzero, reuse the > rmdir waitqueue to block the rmdir until the rcu callback > is called. > > Signed-off-by: Colin Cross <ccross@xxxxxxxxxxx> > --- > > This patch is similar to what you described. The main differences are > that I used a new atomic to handle the rmdir case, and I converted > check_for_release to be callable in softirq context rather than schedule > work in free_css_set_rcu. Your css_set scanning in rmdir sounds better, > I'll take another look at that. Is there any problem with disabling irqs > with spin_lock_irqsave in check_for_release? > > include/linux/cgroup.h | 6 ++ > kernel/cgroup.c | 124 ++++++++++++++++++++++++++++-------------------- > 2 files changed, 78 insertions(+), 52 deletions(-) > Colin, what became of this patch? I see this in your Tegra tree for Android. http://android.git.kernel.org/?p=kernel/tegra.git;a=commit;h=05946a1e0fdb011ac0e6638ee60b181c584f127b I looked in linux-next but didn't see it there. This resolves a performance issue on MSM SMP so I'm curious if this is going upstream. Thanks. - Bryan -- Sent by an employee of the Qualcomm Innovation Center, Inc. The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum. _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers
