Re: [PATCH v2 3/6] x86/time: implement tsc as clocksource

[Joao Martins <joao.m.martins@oracle.com>]

[snip]

>> diff --git a/xen/arch/x86/time.c b/xen/arch/x86/time.c
>> index ed4ed24..2602dda 100644
>> --- a/xen/arch/x86/time.c
>> +++ b/xen/arch/x86/time.c
>> @@ -432,6 +432,63 @@ uint64_t ns_to_acpi_pm_tick(uint64_t ns)
>>  }
>>  
>>  /************************************************************
>> + * PLATFORM TIMER 4: TSC
>> + */
>> +static u64 tsc_freq;
>> +static unsigned long tsc_max_warp;
>> +static void tsc_check_reliability(void);
>> +
>> +static int __init init_tsctimer(struct platform_timesource *pts)
>> +{
>> +    bool_t tsc_reliable = 0;
> 
> No need to set it to zero.
OK.

>> +
>> +    tsc_check_reliability();
> 
> This has been already called by verify_tsc_reliability which calls this
> function. Should we set tsc_max_warp to zero before calling it?
Ah, correct. But may be it's not necessary to run the tsc_check_reliability here
at all as what I am doing is ineficient. See my other comment below.

> 
>> +
>> +    if ( tsc_max_warp > 0 )
>> +    {
>> +        tsc_reliable = 0;
> 
> Ditto. It is by default zero.
OK.

> 
>> +        printk(XENLOG_INFO "TSC: didn't passed warp test\n");
> 
> So the earlier test by verify_tsc_reliability did already this check and
> printed this out - and also cleared the X86_FEATURE_TSC_RELIABLE.
> 
> So can this check above be removed then?
> 
> Or are you thinking to ditch what verify_tsc_reliability does?
> 
I had the tsc_check_reliability here because TSC could still be deemed reliable
for max_cstate <= 2 or with CONSTANT_TSC + NONSTOP_TSC. The way I have it, the
most likely scenario (i.e. having TSC_RELIABLE) would run twice. Perhaps a
better way of doing this would be to run the warp test solely on
verify_tsc_reliability() in all possible conditions to be deemed reliable? And
then I could even remove almost the whole init_tsctimer if it was to be called
when no warps are observed.

>> +    }
>> +    else if ( boot_cpu_has(X86_FEATURE_TSC_RELIABLE) ||
>> +              (boot_cpu_has(X86_FEATURE_CONSTANT_TSC) &&
>> +               boot_cpu_has(X86_FEATURE_NONSTOP_TSC)) )
>> +    {
>> +        tsc_reliable = 1;
>> +    }
>> +    else if ( boot_cpu_has(X86_FEATURE_CONSTANT_TSC) )
>> +    {
>> +        tsc_reliable = (max_cstate <= 2);
>> +
>> +        if ( tsc_reliable )
>> +            printk(XENLOG_INFO "TSC: no deep Cstates, deemed reliable\n");
>> +        else
>> +            printk(XENLOG_INFO "TSC: deep Cstates possible, so not reliable\n");
>> +    }
>> +
>> +    pts->frequency = tsc_freq;
>> +    return tsc_reliable;
>> +}
>> +
>> +static u64 read_tsc(void)
>> +{
>> +    return rdtsc();
>> +}
>> +
>> +static void resume_tsctimer(struct platform_timesource *pts)
>> +{
>> +}
>> +
>> +static struct platform_timesource __initdata plt_tsc =
>> +{
>> +    .id = "tsc",
>> +    .name = "TSC",
>> +    .read_counter = read_tsc,
>> +    .counter_bits = 64,
>> +    .init = init_tsctimer,
> 
> Could you add a note in here:
> 
> /* Not called by init_platform_timer as it is not on the plt_timers array. */
> 
OK, I fixed that.

>> +    .resume = resume_tsctimer,
>> +};
>> +
>> +/************************************************************
>>   * GENERIC PLATFORM TIMER INFRASTRUCTURE
>>   */
>>  
>> @@ -533,6 +590,21 @@ static void resume_platform_timer(void)
>>      plt_stamp = plt_src.read_counter();
>>  }
>>  
>> +static void __init reset_platform_timer(void)
>> +{
>> +    /* Deactivate any timers running */
>> +    kill_timer(&plt_overflow_timer);
>> +    kill_timer(&calibration_timer);
>> +
>> +    /* Reset counters and stamps */
>> +    spin_lock_irq(&platform_timer_lock);
>> +    plt_stamp = 0;
>> +    plt_stamp64 = 0;
>> +    platform_timer_stamp = 0;
>> +    stime_platform_stamp = 0;
>> +    spin_unlock_irq(&platform_timer_lock);
>> +}
>> +
>>  static int __init try_platform_timer(struct platform_timesource *pts)
>>  {
>>      int rc = -1;
>> @@ -541,6 +613,10 @@ static int __init try_platform_timer(struct platform_timesource *pts)
>>      if ( rc <= 0 )
>>          return rc;
>>  
>> +    /* We have a platform timesource already so reset it */
>> +    if ( plt_src.counter_bits != 0 )
>> +        reset_platform_timer();
>> +
>>      plt_mask = (u64)~0ull >> (64 - pts->counter_bits);
>>  
>>      set_time_scale(&plt_scale, pts->frequency);
>> @@ -566,7 +642,9 @@ static void __init init_platform_timer(void)
>>      struct platform_timesource *pts = NULL;
>>      int i, rc = -1;
>>  
>> -    if ( opt_clocksource[0] != '\0' )
>> +    /* clocksource=tsc is initialized later when all CPUS are up */
> 
> Perhaps:
> /* clocksource=tsc is initialized via __initcalls (when CPUs are up). */ ?
> 
It's clearer indeed. Fixed that too.

>> +    if ( (opt_clocksource[0] != '\0') &&
>> +         (strcmp(opt_clocksource, "tsc") != 0) )
>>      {
>>          for ( i = 0; i < ARRAY_SIZE(plt_timers); i++ )
>>          {
>> @@ -1192,7 +1270,7 @@ static void check_tsc_warp(unsigned long tsc_khz, unsigned long *max_warp)
>>      }
>>  }
>>  
>> -static unsigned long tsc_max_warp, tsc_check_count;
>> +static unsigned long tsc_check_count;
>>  static cpumask_t tsc_check_cpumask;
>>  
>>  static void tsc_check_slave(void *unused)
>> @@ -1437,6 +1515,20 @@ static int __init verify_tsc_reliability(void)
>>          }
>>      }
>>  
>> +    if ( !strcmp(opt_clocksource, "tsc") )
>> +    {
>> +        if ( try_platform_timer(&plt_tsc) > 0 )
>> +        {
>> +            printk(XENLOG_INFO "Switched to Platform timer %s TSC\n",
>> +                   freq_string(plt_src.frequency));
>> +
>> +            init_percpu_time();
>> +
>> +            init_timer(&calibration_timer, time_calibration, NULL, 0);
>> +            set_timer(&calibration_timer, NOW() + EPOCH);
>> +        }
>> +    }
>> +
>>      return 0;
>>  }
>>  __initcall(verify_tsc_reliability);
>> @@ -1476,6 +1568,7 @@ void __init early_time_init(void)
>>      struct cpu_time *t = &this_cpu(cpu_time);
>>      u64 tmp = init_pit_and_calibrate_tsc();
>>  
>> +    tsc_freq = tmp;
>>      set_time_scale(&t->tsc_scale, tmp);
>>      t->local_tsc_stamp = boot_tsc_stamp;
>>  
>> -- 
>> 2.1.4

_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xen.org
http://lists.xen.org/xen-devel