[Xen-devel] RE: [PATCH]x86: add a range for hpet broadcast

["Wei, Gang" <gang.wei@xxxxxxxxx>]

On a Xeon 5500 server w/ 2S/8C/16T, w/ HT off, starting 8 rhel5 UP hvm guests, 
idling, I saw 22W (10%) power saving after apply this patch and specify 
timer_slop=1ms on xen grub line. It saves 10W more than the case only specify 
timer_slop=1ms but w\o this patch.

Yes, your suggestion do remove the double dipping. I will give it a try.

Jimmy

Keir Fraser wrote:
> How much of a win is this? The per-cpu timer_deadline is already
> calculated based on slop, so doing it again in hpet.c is kind of like
> double dipping. I think we can validly do some improvements in hpet.c
> however: e.g., by exposing a per-cpu timer deadline range
> (deadline_start,deadline_end) and setting up HPET to fire on the
> earliest deadline_end. Then broadcast to all CPUs with deadline_start
> < NOW() when the HPET fires. 
> 
> The deadline range would be computed as follows in timer.c, in the
> !ts->overflow case in the softirq handler:
> timer_deadline_start = start (i.e., same as timer_deadline today)
> timer_deadline_end = end
> In the (incredibly uncommon) ts->overflow case we can just set
> timer_deadline_start=timer_deadline_end=timer_deadline.
> 
> Perhaps give that a go: I would find that more acceptable at least,
> but all of this really depends on what benchmark improvements you are
> seeing. 
> 
>  -- Keir
> 
> On 09/12/2009 09:33, "Wei, Gang" <gang.wei@xxxxxxxxx> wrote:
> 
>> x86: add a range for hpet broadcast
>> 
>> Apply a range timer like range to hpet broadcast, so that timer
>> expires within timer_slop ns across idle CPUs are capable to be
>> aligned to reduce hpet intrs, and save idle power. 
>> 
>> Signed-off-by: Wei Gang <gang.wei@xxxxxxxxx>

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