Re: [Qemu-devel] arm mptimer implementation - why prescaler is multiply by 10?

[Dmitry Osipenko <digetx@gmail.com>]

27.10.2015 21:01, Peter Crosthwaite пишет:
>
>
> On Tue, Oct 27, 2015 at 7:19 AM, Dmitry Osipenko <digetx@gmail.com
> <mailto:digetx@gmail.com>> wrote:
>
>     27.10.2015 16:48, Krzeminski, Marcin (Nokia - PL/Wroclaw) пишет:
>
>         Hello,
>         I am playing with U-Boot on ARM under qemu.
>         U-boot uses mptimer, and under qemu one second takes about 1 in real world.
>         At the moment it seem that in u-boot is ok, so I have question about
>         below function.
>         Why prescaler value is multiply by 10?
>         static inline uint64_t a9_gtimer_get_conv(A9GTimerState *s)
>         {
>               uint64_t prescale = extract32(s->control, R_CONTROL_PRESCALER_SHIFT,
>                                             R_CONTROL_PRESCALER_LEN);
>               return (prescale + 1) * 10;
>         }
>         Regards,
>         Marcin
>
>
>     Hello Marcin,
>
>      From my observation, Linux kernel is booting noticeably faster in the
>     emulated guest and host machine CPU usage is lower if we "artificially"
>     slowdown the MPtimer. You really shouldn't use it for the RTC, so doing that
>     trick shouldn't affect guest behavior.
>
>     However, maybe there is some other rational behind it and Peter C and/or
>     Peter M might know better.
>
>
> So I do wonder whether with your ptimer conversion this will be obsoleted, as
> the rate limiter there may do the work for us.
>
> Regards,
> Peter
>
>     --
>     Dmitry
>
>

You might be right, I haven't tried it without prescale multiplier with recent 
ptimer fixes. Will try and report back.

-- 
Dmitry