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Date: Fri, 19 Dec 2008 21:02:00 +0100
From: Bartlomiej Zolnierkiewicz <bzolnier@...il.com>
To: Borislav Petkov <borislav.petkov@....com>
Cc: Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
Andreas Herrmann <andreas.herrmann3@....com>,
linux-kernel@...r.kernel.org
Subject: Re: [RESEND PATCH] TSC: resync TSCs on AMD CPUs
On Monday 08 December 2008, Borislav Petkov wrote:
> Hi Ingo, hi Thomas,
>
> please consider for inclusion into .29. This patch has been rediffed against today's tip.
Ingo? Thomas?
This patch seem to have fallen through the cracks...
[ I don't mean to hurry you but it awaits for any reply since
initial posting on 10th November... ]
> ---
> From: Borislav Petkov <borislav.petkov@....com>
> Date: Mon, 08 Dec 2008 18:18:40 +0100
> Subject: [RESEND PATCH] TSC: resync TSCs on AMD CPUs
>
> Although AMD Fam10h CPUs and later have an invariant timestamp counter,
> there's the distant possibility for the application processors to start
> their TSCs shortly after the bootstrapping CPU thus causing a delta
> between the timestamps and fail the initial TSC check. This patch fixes
> that by updating the TSC of each AP with a delta value relative to the
> BSP and then restarting the TSC synchronization test.
>
> update_tsc bits reused from Michael Davidson's patch
> (http://www.gossamer-threads.com/lists/linux/kernel/977166)
>
> Signed-off-by: Borislav Petkov <borislav.petkov@....com>
> Reviewed-by: Andreas Herrmann <andreas.herrmann3@....com>
> Tested-by: Andreas Herrmann <andreas.herrmann3@....com>
> ---
> arch/x86/include/asm/tsc.h | 14 +++++++
> arch/x86/kernel/tsc_sync.c | 94 +++++++++++++++++++++++++++++++++++++++-----
> 2 files changed, 98 insertions(+), 10 deletions(-)
>
> diff --git a/arch/x86/include/asm/tsc.h b/arch/x86/include/asm/tsc.h
> index 9cd83a8..f1e871f 100644
> --- a/arch/x86/include/asm/tsc.h
> +++ b/arch/x86/include/asm/tsc.h
> @@ -9,6 +9,20 @@
> #define NS_SCALE 10 /* 2^10, carefully chosen */
> #define US_SCALE 32 /* 2^32, arbitralrily chosen */
>
> +
> +#define update_tsc(wrmsr, delta) \
> +({ \
> + asm volatile( \
> + "movl $0x10, %%ecx\n\t" \
> + "rdmsr\n\t" \
> + "addl %%edi, %%eax\n\t" \
> + "adcl %%esi, %%edx\n\t" \
> + wrmsr "\n\t" \
> + : /* no output */ \
> + : "D" ((u32)delta), "S"((u32)(delta >> 32)) \
> + : "ax", "cx", "dx", "cc"); \
> +})
> +
> /*
> * Standard way to access the cycle counter.
> */
> diff --git a/arch/x86/kernel/tsc_sync.c b/arch/x86/kernel/tsc_sync.c
> index 1c0dfbc..5fc4092 100644
> --- a/arch/x86/kernel/tsc_sync.c
> +++ b/arch/x86/kernel/tsc_sync.c
> @@ -28,15 +28,28 @@
> static __cpuinitdata atomic_t start_count;
> static __cpuinitdata atomic_t stop_count;
>
> +/* resync counters */
> +static __cpuinitdata atomic_t resync, resync_ran;
> +
> /*
> * We use a raw spinlock in this exceptional case, because
> * we want to have the fastest, inlined, non-debug version
> * of a critical section, to be able to prove TSC time-warps:
> */
> static __cpuinitdata raw_spinlock_t sync_lock = __RAW_SPIN_LOCK_UNLOCKED;
> +static __cpuinitdata raw_spinlock_t resync_lock = __RAW_SPIN_LOCK_UNLOCKED;
> static __cpuinitdata cycles_t last_tsc;
> static __cpuinitdata cycles_t max_warp;
> -static __cpuinitdata int nr_warps;
> +static __cpuinitdata int nr_warps, last_cpu;
> +
> +int cpu_can_resync(void)
> +{
> + if (boot_cpu_has(X86_FEATURE_CONSTANT_TSC) &&
> + boot_cpu_data.x86_vendor == X86_VENDOR_AMD)
> + return 1;
> +
> + return 0;
> +}
>
> /*
> * TSC-warp measurement loop running on both CPUs:
> @@ -89,6 +102,13 @@ static __cpuinit void check_tsc_warp(void)
> __raw_spin_lock(&sync_lock);
> max_warp = max(max_warp, prev - now);
> nr_warps++;
> +
> + /*
> + * handle the highly unlikely event of some application
> + * processor starting its tsc earlier than the
> + * bootstrapping one.
> + */
> + last_cpu = raw_smp_processor_id();
> __raw_spin_unlock(&sync_lock);
> }
> }
> @@ -97,6 +117,36 @@ static __cpuinit void check_tsc_warp(void)
> now-start, end-start);
> }
>
> +void __cpuinit resync_tsc(void)
> +{
> + cycles_t sample_start, sample_stop;
> + unsigned long flags;
> + long long delta;
> + int sign = last_cpu ? 1 : -1;
> +
> + local_irq_save(flags);
> + __raw_spin_lock(&resync_lock);
> +
> + /* sample ops timing taking to write the TSC msr */
> + sample_start = get_cycles();
> + update_tsc("", max_warp);
> + sample_stop = get_cycles();
> +
> + delta = sign * ((sample_stop - sample_start) + max_warp);
> +
> + update_tsc("wrmsr", delta);
> +
> + atomic_set(&resync_ran, 1);
> + atomic_set(&resync, 0);
> +
> + nr_warps = 0;
> + max_warp = 0;
> + last_tsc = 0;
> +
> + __raw_spin_unlock(&resync_lock);
> + local_irq_restore(flags);
> +}
> +
> /*
> * Source CPU calls into this - it waits for the freshly booted
> * target CPU to arrive and then starts the measurement:
> @@ -105,6 +155,7 @@ void __cpuinit check_tsc_sync_source(int cpu)
> {
> int cpus = 2;
>
> +restart_src:
> /*
> * No need to check if we already know that the TSC is not
> * synchronized:
> @@ -136,26 +187,42 @@ void __cpuinit check_tsc_sync_source(int cpu)
> cpu_relax();
>
> if (nr_warps) {
> - printk("\n");
> - printk(KERN_WARNING "Measured %Ld cycles TSC warp between CPUs,"
> - " turning off TSC clock.\n", max_warp);
> - mark_tsc_unstable("check_tsc_sync_source failed");
> + if (cpu_can_resync() && !atomic_read(&resync_ran)) {
> +
> + printk(KERN_CONT " failed.\n");
> + printk(KERN_WARNING "TSC out of sync, resynching.\n");
> + atomic_set(&start_count, 0);
> +
> + /* start resync sequence */
> + atomic_set(&resync, 1);
> +
> + goto restart_src;
> + } else {
> + printk(KERN_CONT "\n");
> + printk(KERN_WARNING "Measured %lld cycles TSC warp "
> + "between CPUs, turning off TSC clock.\n",
> + max_warp);
> + mark_tsc_unstable("check_tsc_sync_source failed");
> + }
> } else {
> printk(" passed.\n");
> }
>
> /*
> + * Let the target continue with the bootup:
> + */
> + atomic_inc(&stop_count);
> +
> + /*
> * Reset it - just in case we boot another CPU later:
> */
> atomic_set(&start_count, 0);
> + atomic_set(&resync_ran, 0);
> nr_warps = 0;
> max_warp = 0;
> last_tsc = 0;
>
> - /*
> - * Let the target continue with the bootup:
> - */
> - atomic_inc(&stop_count);
> +
> }
>
> /*
> @@ -165,6 +232,10 @@ void __cpuinit check_tsc_sync_target(void)
> {
> int cpus = 2;
>
> +restart_tgt:
> + if (atomic_read(&resync))
> + resync_tsc();
> +
> if (unsynchronized_tsc())
> return;
>
> @@ -186,8 +257,11 @@ void __cpuinit check_tsc_sync_target(void)
> /*
> * Wait for the source CPU to print stuff:
> */
> - while (atomic_read(&stop_count) != cpus)
> + while (atomic_read(&stop_count) != cpus) {
> + if (atomic_read(&resync) && (!atomic_read(&resync_ran)))
> + goto restart_tgt;
> cpu_relax();
> + }
> }
> #undef NR_LOOPS
>
> --
> 1.6.0.2
>
> --
> Regards/Gruss,
> Boris.
>
> Advanced Micro Devices, Inc.
> Operating System Research Center
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