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Re: [Qemu-ppc] [PATCH] eventfd: making it thread safe
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-ppc] [PATCH] eventfd: making it thread safe |
Date: |
Wed, 18 Jul 2012 15:22:02 +0300 |
On Wed, Jul 18, 2012 at 10:08:53PM +1000, Alexey Kardashevskiy wrote:
> QEMU uses IO handlers to run select() in the main loop.
> The handlers list is managed by qemu_set_fd_handler() helper
> which works fine when called from the main thread as it is
> called not when select() is waiting.
when select() is not waiting?
>
> However IO handlers list can be changed in the thread other than
> the main one doing os_host_main_loop_wait(), for example, as a result
> of a hypercall which changes PCI config space (VFIO on POWER is the case)
So the problem is only with VFIO? Can it affect vhost-net?
> and enables/disabled MSI/MSIX which closes/creates eventfd handles.
There doesn't seem to be a notification in case an fd is
deleted. It's probably not at all urgent to remove
an fd from select - why do you mention closing handles?
> If the main loop is waiting on such eventfd, it has to be restarted.
Do you really mean 'should be waiting on the newly created
eventfd'?
> The patch adds the qemu_notify_event() call to interrupt select()
> and make main_loop() to restart select()
s/and make main_loop() to restart/to make main_loop() restart/?
> with the updated IO
> handlers list.
>
> Signed-off-by: Alexey Kardashevskiy <address@hidden>
> Reviewed-by: Paolo Bonzini <address@hidden>
> ---
> iohandler.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/iohandler.c b/iohandler.c
> index 3c74de6..dea4355 100644
> --- a/iohandler.c
> +++ b/iohandler.c
> @@ -77,6 +77,7 @@ int qemu_set_fd_handler2(int fd,
> ioh->fd_write = fd_write;
> ioh->opaque = opaque;
> ioh->deleted = 0;
> + qemu_notify_event();
> }
> return 0;
> }
> --
> 1.7.10.4