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Re: [Qemu-devel] Linux kernel polling for QEMU
From: |
Fam Zheng |
Subject: |
Re: [Qemu-devel] Linux kernel polling for QEMU |
Date: |
Tue, 29 Nov 2016 21:24:10 +0800 |
User-agent: |
Mutt/1.7.1 (2016-10-04) |
On Tue, 11/29 12:17, Paolo Bonzini wrote:
>
>
> On 29/11/2016 11:32, Fam Zheng wrote:
> >
> > The kernel change will be a new prctl operation (should it be a different
> > syscall to extend?) to register a new type of eventfd called "idle eventfd":
> >
> > prctl(PR_ADD_IDLE_EVENTFD, int eventfd);
> > prctl(PR_DEL_IDLE_EVENTFD, int eventfd);
> >
> > It will be notified by kernel each time when the thread's local core has no
> > runnable threads (i.e., entering idle state).
> >
> > QEMU can then add this eventfd to its event loop when it has events to
> > poll, and
> > watch virtqueue/linux-aio memory from userspace in the fd handlers.
> > Effectiely,
> > if a ppoll() would have blocked because there are no new events, it could
> > now
> > return immediately because of idle_eventfd events, and do the idle polling.
>
> This has two issues:
>
> * it only reports the leading edge of single_task_running(). Is it also
> useful to stop polling on the trailing edge?
QEMU can clear the eventfd right after event firing so I don't think it is
necessary.
>
> * it still needs a system call before polling is entered. Ideally, QEMU
> could run without any system call while in polling mode.
>
> Another possibility is to add a system call for single_task_running().
> It should be simple enough that you can implement it in the vDSO and
> avoid a context switch. There are convenient hooking points in
> add_nr_running and sub_nr_running.
That sounds good!
Fam
- Re: [Qemu-devel] Linux kernel polling for QEMU, (continued)
- Re: [Qemu-devel] Linux kernel polling for QEMU, Christian Borntraeger, 2016/11/29
- Re: [Qemu-devel] Linux kernel polling for QEMU, Fam Zheng, 2016/11/29
- Re: [Qemu-devel] Linux kernel polling for QEMU, Paolo Bonzini, 2016/11/29
- Re: [Qemu-devel] Linux kernel polling for QEMU,
Fam Zheng <=
- Re: [Qemu-devel] Linux kernel polling for QEMU, Paolo Bonzini, 2016/11/29
- Re: [Qemu-devel] Linux kernel polling for QEMU, Fam Zheng, 2016/11/29
- Re: [Qemu-devel] Linux kernel polling for QEMU, Andrew Jones, 2016/11/29
- Re: [Qemu-devel] Linux kernel polling for QEMU, Fam Zheng, 2016/11/29
- Re: [Qemu-devel] Linux kernel polling for QEMU, Andrew Jones, 2016/11/29
- Re: [Qemu-devel] Linux kernel polling for QEMU, Paolo Bonzini, 2016/11/29
- Re: [Qemu-devel] Linux kernel polling for QEMU, Andrew Jones, 2016/11/29
- Re: [Qemu-devel] Linux kernel polling for QEMU, Peter Maydell, 2016/11/30
- Re: [Qemu-devel] Linux kernel polling for QEMU, Andrew Jones, 2016/11/30
- Re: [Qemu-devel] Linux kernel polling for QEMU, Peter Maydell, 2016/11/30