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Re: [Qemu-devel] timer issue on 1.7.0 and later
From: |
Alex Bligh |
Subject: |
Re: [Qemu-devel] timer issue on 1.7.0 and later |
Date: |
Thu, 13 Feb 2014 16:31:32 +0000 |
On 13 Feb 2014, at 16:20, Peter Maydell wrote:
> On 13 February 2014 16:09, Alex Bligh <address@hidden> wrote:
>> I suspect the issue is not walking the lists, but calling
>> qemu_notify, breaking out of mainloop select etc. etc.; that
>> happens on a timer_modify but not on a timer_del. We could
>> fix this so that it only happened if the timer's expiry
>> time was reduced in timer_mod (I think).
>
> Surely you only want to do all that work if the fiddling
> with the timer means the next most immediate deadline
> has changed? If you have two timers, and A is going to
> expire before B, then even reducing B's expiry time shouldn't
> trigger renotifying unless it's reduced so much it will
> expire before A.
Correct.
The current code (timer_mod_ns_locked) runs the rearm code
if the modified timer is at the front of the timer queue
(only). So if you modify B (in your example above) whether
you extend or reduce the time, it will only 'rearm' if
B now occurs before A. However, if you modify A, it will
currently rearm whether you reduce the expiry time of
A (correct) or whether you extend it so long as it doesn't
now expire after B (this could perhaps be optimised).
So it's not quite as bad as you think.
--
Alex Bligh
- [Qemu-devel] timer issue on 1.7.0 and later, Rob Herring, 2014/02/07
- Re: [Qemu-devel] timer issue on 1.7.0 and later, Alex Bligh, 2014/02/08
- Re: [Qemu-devel] timer issue on 1.7.0 and later, Paolo Bonzini, 2014/02/08
- Re: [Qemu-devel] timer issue on 1.7.0 and later, Alex Bligh, 2014/02/08
- Re: [Qemu-devel] timer issue on 1.7.0 and later, Rob Herring, 2014/02/10
- Re: [Qemu-devel] timer issue on 1.7.0 and later, Alex Bligh, 2014/02/10
- Re: [Qemu-devel] timer issue on 1.7.0 and later, Peter Maydell, 2014/02/13
- Re: [Qemu-devel] timer issue on 1.7.0 and later, Alex Bligh, 2014/02/13
- Re: [Qemu-devel] timer issue on 1.7.0 and later, Peter Maydell, 2014/02/13
- Re: [Qemu-devel] timer issue on 1.7.0 and later,
Alex Bligh <=
- Re: [Qemu-devel] timer issue on 1.7.0 and later, Peter Maydell, 2014/02/13