Re: [Qemu-devel] [PATCH 0/3] qemu-timer: make QEMUTimer functions thread-safe

[Jan Kiszka]

On 2013-07-05 14:39, Stefan Hajnoczi wrote:
> This series makes the following functions thread-safe:
> 
>   qemu_mod_timer_ns()
>   qemu_mod_timer()
>   qemu_del_timer()
>   qemu_timer_pending()
> 
> The following were already thread-safe:
> 
>   qemu_free_timer()
>   qemu_new_timer()
>   qemu_timer_expired()
> 
> Now it is possible to use QEMUTimer outside the QEMU global mutex.  Timer
> callbacks are still invoked from the main loop.  If a thread wishes to run
> timer callbacks it must use a thread-safe QEMUBH (which Ping Fan Liu is 
> working
> on).

What do you mean with this? We need main-loop independent timers for any
task that depends on timely alarm delivery. Do your patches keep this in
mind as well?

> 
> Note that host_clock is not thread-safe because it keeps state and invokes
> reset notifiers.  Device emulation threads mostly care about vm_clock, so this
> is not a problem.

I suppose you know that vm_clock cannot be read outside BQL yet due to
timers_state and, under TCG, icount. Any ideas regarding this already? I
didn't have to solve that problem so far as I only need CLOCK_REALTIME
outside BQL.

Jan

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