Re: [PATCH v1] rtc/mc146818rtc: improve rtc performance

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Jul 24, 2023 at 04:54:22PM +0800, Evanzhang wrote:
> under heavy workloads,irq_coalesced could up to 30+,
> after modification EXTERNAL_INTERRUPT reduce by 40%
> 
> before:
> Analyze events for all VMs, all VCPUs:
>              VM-EXIT    Samples  Samples%     Time%
> 
>        EPT_VIOLATION    9833984    63.41%    15.96%
>       IO_INSTRUCTION    2160843    13.93%    50.07%
>   EXTERNAL_INTERRUPT    1949267    12.57%     0.89%
>           APIC_WRITE     767795     4.95%     0.55%
>          EOI_INDUCED     615308     3.97%     0.30%
>                  HLT     130821     0.84%    31.77%
> 
> after:
> Analyze events for all VMs, all VCPUs:
>              VM-EXIT    Samples  Samples%     Time%
> 
>        EPT_VIOLATION    5238031    50.91%     6.44%
>       IO_INSTRUCTION    2257658    21.94%    54.88%
>   EXTERNAL_INTERRUPT    1160086    11.28%     0.61%
>           APIC_WRITE     780454     7.59%     0.54%
>          EOI_INDUCED     615309     5.98%     0.28%
>                  HLT     179703     1.75%    36.87%
> 
> Signed-off-by: Evanzhang <Evanzhang@archeros.com>



Paolo do you mind picking this old patch up?

Reviewed-by: Michael S. Tsirkin <mst@redhat.com>

> ---
>  hw/rtc/mc146818rtc.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/rtc/mc146818rtc.c b/hw/rtc/mc146818rtc.c
> index c27c362..2995078 100644
> --- a/hw/rtc/mc146818rtc.c
> +++ b/hw/rtc/mc146818rtc.c
> @@ -96,8 +96,8 @@ static void rtc_coalesced_timer_update(MC146818RtcState *s)
>      if (s->irq_coalesced == 0) {
>          timer_del(s->coalesced_timer);
>      } else {
> -        /* divide each RTC interval to 2 - 8 smaller intervals */
> -        int c = MIN(s->irq_coalesced, 7) + 1;
> +        /* divide each RTC interval to 2 - 32 smaller intervals */
> +        int c = MIN(s->irq_coalesced, 31) + 1;
>          int64_t next_clock = qemu_clock_get_ns(rtc_clock) +
>              periodic_clock_to_ns(s->period / c);
>          timer_mod(s->coalesced_timer, next_clock);
> -- 
> 2.9.5