Re: [Qemu-devel] [PATCH] rewrote timer implementation for rtl8139.

[Anthony Liguori <anthony@codemonkey.ws>]

On 02/16/2010 02:35 AM, Frediano Ziglio wrote:
> Add a QEMU timer only when needed (timeout status not set, timeout
> irq wanted and timer set).
>
> This patch is required for Darwin. Patch has been tested under
> FreeBSD, Darwin and Linux.
>
> Signed-off-by: Frediano Ziglio<freddy77@gmail.com>
> ---
>   hw/rtl8139.c |  136 ++++++++++++++++++++++++++++++++++-----------------------
>   1 files changed, 81 insertions(+), 55 deletions(-)
>
> diff --git a/hw/rtl8139.c b/hw/rtl8139.c
> index f04dd54..e43c15c 100644
> --- a/hw/rtl8139.c
> +++ b/hw/rtl8139.c
> @@ -41,6 +41,10 @@
>    *                                  segmentation offloading
>    *                                  Removed slirp.h dependency
>    *                                  Added rx/tx buffer reset when enabling rx/tx operation
> + *
> + *  2010-Feb-04  Frediano Ziglio:   Rewrote timer support using QEMU timer only
> + *                                  when strictly needed (required for for
> + *                                  Darwin)
>    */
>
>   #include "hw.h"
> @@ -60,9 +64,6 @@
>   /* Calculate CRCs properly on Rx packets */
>   #define RTL8139_CALCULATE_RXCRC 1
>
> -/* Uncomment to enable on-board timer interrupts */
> -//#define RTL8139_ONBOARD_TIMER 1
> -
>   #if defined(RTL8139_CALCULATE_RXCRC)
>   /* For crc32 */
>   #include<zlib.h>
> @@ -491,9 +492,12 @@ typedef struct RTL8139State {
>
>       /* PCI interrupt timer */
>       QEMUTimer *timer;
> +    int64_t TimerExpire;
>
>   } RTL8139State;
>
> +static void rtl8139_set_next_tctr_time(RTL8139State *s, int64_t current_time);
> +
>   static void prom9346_decode_command(EEprom9346 *eeprom, uint8_t command)
>   {
>       DEBUG_PRINT(("RTL8139: eeprom command 0x%02x\n", command));
> @@ -2522,7 +2526,9 @@ static void rtl8139_IntrMask_write(RTL8139State *s, uint32_t val)
>
>       s->IntrMask = val;
>
> +    rtl8139_set_next_tctr_time(s, qemu_get_clock(vm_clock));
>       rtl8139_update_irq(s);
> +
>   }
>
>   static uint32_t rtl8139_IntrMask_read(RTL8139State *s)
> @@ -2555,12 +2561,22 @@ static void rtl8139_IntrStatus_write(RTL8139State *s, uint32_t val)
>       rtl8139_update_irq(s);
>
>       s->IntrStatus = newStatus;
> +    /*
> +     * Computing if we miss an interrupt here is not that correct but
> +     * considered that we should have had already an interrupt
> +     * and probably emulated is slower is better to assume this resetting was
> +     * done before testing on previous rtl8139_update_irq lead to IRQ loosing
> +     */
> +    rtl8139_set_next_tctr_time(s, qemu_get_clock(vm_clock));
>       rtl8139_update_irq(s);
> +
>   #endif
>   }
>
>   static uint32_t rtl8139_IntrStatus_read(RTL8139State *s)
>   {
> +    rtl8139_set_next_tctr_time(s, qemu_get_clock(vm_clock));
> +
>       uint32_t ret = s->IntrStatus;
>
>       DEBUG_PRINT(("RTL8139: IntrStatus read(w) val=0x%04x\n", ret));
> @@ -2739,6 +2755,43 @@ static void rtl8139_io_writew(void *opaque, uint8_t addr, uint32_t val)
>       }
>   }
>
> +static void rtl8139_set_next_tctr_time(RTL8139State *s, int64_t current_time)
> +{
> +    DEBUG_PRINT(("RTL8139: entered rtl8139_set_next_tctr_time\n"));
> +
> +    if (s->TimerExpire&&  current_time>= s->TimerExpire) {
> +        s->IntrStatus |= PCSTimeout;
> +        rtl8139_update_irq(s);
> +    }
> +
> +    /* Set QEMU timer only if needed that is
> +     * - TimerInt<>  0 (we have a timer)
> +     * - mask = 1 (we want an interrupt timer)
> +     * - irq = 0  (irq is not already active)
> +     * If any of above change we need to compute timer again
> +     * Also we must check if timer is passed without QEMU timer
> +     */
> +    s->TimerExpire = 0;
> +    if (!s->TimerInt) {
> +        return;
> +    }
> +
> +    int64_t pci_time = muldiv64(current_time - s->TCTR_base, PCI_FREQUENCY,
> +                                get_ticks_per_sec());
> +    uint32_t low_pci = pci_time&  0xffffffff;
>    

Please don't mix variable declarations in code.

> +    pci_time = pci_time - low_pci + s->TimerInt;
> +    if (low_pci>= s->TimerInt) {
> +        pci_time += 0x100000000LL;
> +    }
> +    int64_t next_time = s->TCTR_base + muldiv64(pci_time, get_ticks_per_sec(),
> +                                                PCI_FREQUENCY);
> +    s->TimerExpire = next_time;
> +
> +    if ((s->IntrMask&  PCSTimeout) != 0&&  (s->IntrStatus&  PCSTimeout) == 0) {
> +        qemu_mod_timer(s->timer, next_time);
> +    }
> +}
> +
>   static void rtl8139_io_writel(void *opaque, uint8_t addr, uint32_t val)
>   {
>       RTL8139State *s = opaque;
> @@ -2784,13 +2837,16 @@ static void rtl8139_io_writel(void *opaque, uint8_t addr, uint32_t val)
>
>           case Timer:
>               DEBUG_PRINT(("RTL8139: TCTR Timer reset on write\n"));
> -            s->TCTR = 0;
>               s->TCTR_base = qemu_get_clock(vm_clock);
> +            rtl8139_set_next_tctr_time(s, s->TCTR_base);
>               break;
>
>           case FlashReg:
>               DEBUG_PRINT(("RTL8139: FlashReg TimerInt write val=0x%08x\n", val));
> -            s->TimerInt = val;
> +            if (s->TimerInt != val) {
> +                s->TimerInt = val;
> +                rtl8139_set_next_tctr_time(s, qemu_get_clock(vm_clock));
> +            }
>               break;
>
>           default:
> @@ -3000,7 +3056,8 @@ static uint32_t rtl8139_io_readl(void *opaque, uint8_t addr)
>               break;
>
>           case Timer:
> -            ret = s->TCTR;
> +            ret = muldiv64(qemu_get_clock(vm_clock) - s->TCTR_base,
> +                           PCI_FREQUENCY, get_ticks_per_sec());
>               DEBUG_PRINT(("RTL8139: TCTR Timer read val=0x%08x\n", ret));
>               break;
>
> @@ -3105,6 +3162,7 @@ static uint32_t rtl8139_mmio_readl(void *opaque, target_phys_addr_t addr)
>   static int rtl8139_post_load(void *opaque, int version_id)
>   {
>       RTL8139State* s = opaque;
> +    rtl8139_set_next_tctr_time(s, qemu_get_clock(vm_clock));
>       if (version_id<  4) {
>           s->cplus_enabled = s->CpCmd != 0;
>       }
> @@ -3112,12 +3170,24 @@ static int rtl8139_post_load(void *opaque, int version_id)
>       return 0;
>   }
>
> +static void rtl8139_pre_save(void *opaque)
> +{
> +    RTL8139State* s = opaque;
> +
> +    // set IntrStatus correctly
>    

Please avoid C99 comments.

> +    int64_t current_time = qemu_get_clock(vm_clock);
> +    rtl8139_set_next_tctr_time(s, current_time);
> +    s->TCTR = muldiv64(current_time - s->TCTR_base, PCI_FREQUENCY,
> +                       get_ticks_per_sec());
> +}
>    

Usually, timers have to be saved as part of save/restore in order for 
them to fire correctly when restarted.  I suspect this breaks save/restore.

I'd like to see some performance data too.  I'm concerned that a change 
like this could have a significant impact on performance.

Regards,

Anthony Liguori