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Re: [Qemu-devel] Linux kernel polling for QEMU
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] Linux kernel polling for QEMU |
Date: |
Tue, 29 Nov 2016 12:17:56 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0 |
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?
* 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.
Paolo
- [Qemu-devel] Linux kernel polling for QEMU, Stefan Hajnoczi, 2016/11/24
- 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 <=
- 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, 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