Re: perf hw in kexeced kernel broken in tip

Yinghai Lu
2010-12-08T18:44:15Z

On 12/08/2010 06:59 AM, Peter Zijlstra wrote:
> On Wed, 2010-12-08 at 15:20 +0100, Peter Zijlstra wrote:
>
>>> I wonder if you should reverse these checks. If the bios has the perf
>>> counter enabled, there might be a high chance that it fails the first
>>> check and never gets to the actually bios checks.
>>
>> Ah, good point.
>
> Something like so..
>
> ---
> Subject: perf, x86: Detect broken BIOSes
> From: Peter Zijlstra <a.p.zijlstra@chello.nl>
> Date: Wed Dec 08 15:56:23 CET 2010
>
> Some BIOSes use PMU resources, this is a bug.
>
> Try to detect this, warn about it, and further refuse to touch the
> PMU ourselves.
>
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
> ---
> Index: linux-2.6/arch/x86/kernel/cpu/perf_event.c
> ===================================================================
> --- linux-2.6.orig/arch/x86/kernel/cpu/perf_event.c
> +++ linux-2.6/arch/x86/kernel/cpu/perf_event.c
> @@ -375,15 +375,51 @@ static void release_pmc_hardware(void) {
> static bool check_hw_exists(void)
> {
> u64 val, val_new = 0;
> - int ret = 0;
> + int i, reg, ret = 0;
>
> + /*
> + * Check to see if the BIOS enabled any of the counters, if so
> + * complain and bail.
> + */
> + for (i = 0; i < x86_pmu.num_counters; i++) {
> + reg = x86_pmu.eventsel + i;
> + ret = rdmsrl_safe(reg, &val);
> + if (ret)
> + goto msr_fail;
> + if (val & ARCH_PERFMON_EVENTSEL_ENABLE)
> + goto bios_fail;
> + }
> +
> + for (i = 0; i < x86_pmu.num_counters_fixed; i++) {
> + reg = MSR_ARCH_PERFMON_FIXED_CTR_CTRL;
> + ret = rdmsrl_safe(reg, &val);
> + if (ret)
> + goto msr_fail;
> + if (val & (0x03 << i*4))
> + goto bios_fail;
> + }
> +
> + /*
> + * Now write a value and read it back to see if it matches,
> + * this is needed to detect certain hardware emulators (qemu/kvm)
> + * that don't trap on the MSR access and always return 0s.
> + */
> val = 0xabcdUL;
> - ret |= checking_wrmsrl(x86_pmu.perfctr, val);
> + ret = checking_wrmsrl(x86_pmu.perfctr, val);
> ret |= rdmsrl_safe(x86_pmu.perfctr, &val_new);
> if (ret || val != val_new)
> - return false;
> + goto msr_fail;
>
> return true;
> +
> +bios_fail:
> + printk(KERN_CONT "Broken BIOS detected, software events only.\n");
> + printk(KERN_ERR FW_BUG "invalid MSR: %x=%Lx\n", reg, val);
> + return false;
> +
> +msr_fail:
> + printk(KERN_CONT "Broken PMU hardware detected, software events only.\n");
> + return false;
> }

can you add sth force_... in command line to take over ownership of perf from BIOS or previous kernel ?

then still can use perf etc after we kexec from RHEL or SLES kernel to later kernel ( from 2.6.37)

Thanks

Yinghai

>
> static void reserve_ds_buffers(void);
> @@ -1378,10 +1414,8 @@ int __init init_hw_perf_events(void)
> pmu_check_apic();
>
> /* sanity check that the hardware exists or is emulated */
> - if (!check_hw_exists()) {
> - pr_cont("Broken PMU hardware detected, software events only.\n");
> + if (!check_hw_exists())
> return 0;
> - }
>
> pr_cont("%s PMU driver.\n", x86_pmu.name);
>
>