On 08/01, Gregory Haskins wrote:
>
> On Thu, 2007-08-02 at 00:50 +0400, Oleg Nesterov wrote:
> > On 08/01, Daniel Walker wrote:
> > >
> > > It's translating priorities through the work queues, which doesn't seem
> > > to happen with the current implementation. A high priority, say
> > > SCHED_FIFO priority 99, task may have to wait for a nice -5 work queue
> > > to finish..
> >
> > Why should that task wait?
>
> I assume "that task" = the RT99 task? If so, that is precisely the
> question. It shouldn't wait. ;) With mainline, it is simply queued
> with every other request. There could be an RT40, and a SCHED_NORMAL in
> front of it in the queue that will get processed first. In addition,
> the system could suffer from a priority inversion if some unrelated but
> lower priority task (say RT98) was blocking the workqueue thread from
> making forward progress on the nice -5 job.
>
> To clarify: when a design utilizes a singlethread per workqueue (such as
> in both mainline and this patch), the RT99 will always have to wait
> behind any already dispatched jobs.
It is not that "RT99 will always have to wait". But yes, the work_struct
queued by RT99 has to wait.
> That is a given. However, with
> Daniels patch, two things happen in addition to normal processing.
Yes, I see what the patch does,
> 1) The RT99 task would move ahead in the queue of anything else that was
> also scheduled on the workqueue that is < RT99.
this itself is wrong, breaks flush_workqueue() semantics
> 2) The priority of the workqueue task would be temporarily elevated to
> RT99 so that the currently dispatched task will complete at the same
> priority as the waiter.
_Which_ waiter? I can't understand at all why work_struct should "inherit"
the priority of the task which queued it. This looks just wrong to me,
even if could implement this safely.
Oleg.
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
