On Thu, 2010-05-27 at 14:44 +0200, Oleg Nesterov wrote:
> On 05/27, Michael S. Tsirkin wrote:
> >
> > On Tue, May 18, 2010 at 05:04:51PM -0700, Sridhar Samudrala wrote:
> > > Add a new kernel API to create a singlethread workqueue and attach it's
> > > task to current task's cgroup and cpumask.
> > >
> > > Signed-off-by: Sridhar Samudrala <sri@xxxxxxxxxx>
> >
> > Could someone familiar with workqueue code please comment on whether
> > this patch is suitable for 2.6.35?
> >
> > It is needed to fix the case where vhost user might cause a kernel
> > thread to consume more CPU than allowed by the cgroup.
> > Should I merge it through the vhost tree?
> > Ack for this?
>
> I don't understand the reasons for this patch, but this doesn't matter.
>
> I don't really see any need to change workqueue.c,
>
> > > +static struct task_struct *get_singlethread_wq_task(struct workqueue_struct *wq)
> > > +{
> > > + return (per_cpu_ptr(wq->cpu_wq, singlethread_cpu))->thread;
> > > +}
>
> (Not sure this trivial static helper with the single caller makes sense, but
> see below)
>
> > > +/* Create a singlethread workqueue and attach it's task to the current task's
> > > + * cgroup and set it's cpumask to the current task's cpumask.
> > > + */
> > > +struct workqueue_struct *create_singlethread_workqueue_in_current_cg(char *name)
> > > +{
> > > + struct workqueue_struct *wq;
> > > + struct task_struct *task;
> > > + cpumask_var_t mask;
> > > +
> > > + wq = create_singlethread_workqueue(name);
> > > + if (!wq)
> > > + goto out;
> > > +
> > > + if (!alloc_cpumask_var(&mask, GFP_KERNEL))
> > > + goto err;
> > > +
> > > + if (sched_getaffinity(current->pid, mask))
> > > + goto err;
> > > +
> > > + task = get_singlethread_wq_task(wq);
> > > + if (sched_setaffinity(task->pid, mask))
> > > + goto err;
> > > +
> > > + if (cgroup_attach_task_current_cg(task))
> > > + goto err;
> > > +out:
> > > + return wq;
> > > +err:
> > > + destroy_workqueue(wq);
> > > + wq = NULL;
> > > + goto out;
> > > +}
>
> Instead, cgroup.c (or whoever needs this) can do
>
> struct move_struct {
> struct work_struct work;
> int ret;
> };
>
> static void move_func(struct work_struct *work)
> {
> struct move_struct *move = container_of(...);
>
> if (cgroup_attach_task_current_cg(current))
We are trying to attach the task associated with workqueue to the
current task's cgroup. So what we need is
cgroup_attach_task_current_cg(wq->task);
However there is no interface currently that exports the task associated
with a workqueue. It is hidden in cpu_workqueue_struct and is only
accessible within workqueue.c.
> ret = -EANY;
> }
>
> static struct workqueue_struct *create_singlethread_workqueue_in_current_cg(char *name)
> {
> struct workqueue_struct *wq;
> struct move_struct move = {
> .work = __WORK_INITIALIZER(move_func);
> };
>
> wq = create_singlethread_workqueue(name);
> if (!wq)
> return NULL;
>
> queue_work(&move.work);
> flush_work(&move.work);
>
> if (move.ret) {
> destroy_workqueue(wq);
> wq = NULL;
> }
>
> return wq;
> }
>
> Or. Just export wq_per_cpu() from workqueue.c (probably with a better name) and
> use it like the patch does.
This requires that struct cpu_workqueue_struct and struct
workqueue_struct are made externally visible by moving them to
kernel/workqueue.h.
Instead what about adding the simple helper get_singlethread_wq_task()
in workqueue.c and exporting it.
I can add create_singlethread_workqueue_in_current_cg() to cgroup.c
using this helper routine.
Thanks
Sridhar
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