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am 19.11.2010 schrieb "Jan Beulich <JBeulich@xxxxxxxxxx>":
> >>> On 19.11.10 at 11:29, Dietmar Hahn <dietmar.hahn@xxxxxxxxxxxxxx> wrote:
> > +/*
> > + * QUIRK to workaround an issue on Nehalem processors currently seen
> > + * on family 6 cpus E5520 (model 26) and X7542 (model 46).
> > + * The issue leads to endless NMI loops on the processor.
> > + * If a counter triggers an NMI and while the NMI handler is running another
> > + * counter overflows the second counter triggers endless new NMIs.
> > + * A solution is to read all flagged counters and if the value is 0 write
> > + * 1 into it.
> > + */
I will try to improve the comment.
>
> Two things I don't understand here: One is that I can't see how
> from the NMI handler control would get to
> core2_vpmu_do_interrupt() - afaics, this gets called only in the
> context of the (vectored) smp_pmu_apic_interrupt(). The other
> is that if nested interrupts occur, how would you prevent this
> by writing ones into zero counters? That is, in the best case I
> could see this shrinking the window within which unintended
> nested interrupts would occur. Or is it that the secondary
> interrupts only occur after the first one returned? Is this (mis-)
> behavior documented somewhere?
>
> > +static int is_nmi_quirk;
>
> bool_t __read_mostly?
Yes, would be better.
>
> > +
> > +static void check_nmi_quirk(void)
> > +{
> > + u8 family = current_cpu_data.x86;
> > + u8 cpu_model = current_cpu_data.x86_model;
> > + is_nmi_quirk = 0;
> > + if ( family == 6 )
> > + {
> > + if ( cpu_model == 46 || cpu_model == 26 )
> > + is_nmi_quirk = 1;
> > + }
> > +}
> > +
> > +static int core2_get_pmc_count(void);
> > +static void handle_nmi_quirk(u64 msr_content)
> > +{
> > + int num_gen_pmc = core2_get_pmc_count();
> > + int num_fix_pmc = 3;
> > + int i;
> > + u64 val;
> > +
> > + if ( !is_nmi_quirk )
> > + return;
> > +
> > + val = msr_content & ((1 << num_gen_pmc) - 1);
>
> What's the point of masking if the subsequent loop looks at the
> bottom so many bits only anyway?
Bits 0-31 flag the overflow of the general counters (currently max 4) and 32-63
flag the overflow of the fixed counter (currently max 3).
Yes the first mask is not necessary, maybe a comment would be better?
>
> > + for ( i = 0; i < num_gen_pmc; i++ )
> > + {
> > + if ( val & 0x1 )
> > + {
> > + u64 cnt;
> > + rdmsrl(MSR_P6_PERFCTR0 + i, cnt);
> > + if ( cnt == 0 )
> > + wrmsrl(MSR_P6_PERFCTR0 + i, 1);
> > + }
> > + val >>= 1;
> > + }
> > + val = (msr_content >> 32) & ((1 << num_fix_pmc) - 1);
>
> Same here.
>
> > + for ( i = 0; i < num_fix_pmc; i++ )
> > + {
> > + if ( val & 0x1 )
> > + {
> > + u64 cnt;
> > + rdmsrl(MSR_CORE_PERF_FIXED_CTR0 + i, cnt);
> > + if ( cnt == 0 )
> > + wrmsrl(MSR_CORE_PERF_FIXED_CTR0 + i, 1);
> > + }
> > + val >>= 1;
> > + }
> > +}
> > +
> > +#define CHECK_HANDLE_NMI_QUIRK(msr_content) \
> > + if ( is_nmi_quirk ) \
> > + handle_nmi_quirk(msr_content);
> > +
>
> Why do you need a macro here if you use it only once?
I did this only to have as few impact on the existing code as possible.
I will remove it.
Thanks.
Dietmar.
>
> > u32 core2_counters_msr[] = {
> > MSR_CORE_PERF_FIXED_CTR0,
> > MSR_CORE_PERF_FIXED_CTR1,
> > @@ -494,6 +558,9 @@
> > rdmsrl(MSR_CORE_PERF_GLOBAL_STATUS, msr_content);
> > if ( !msr_content )
> > return 0;
> > +
> > + CHECK_HANDLE_NMI_QUIRK(msr_content)
> > +
> > core2_vpmu_cxt->global_ovf_status |= msr_content;
> > msr_content = 0xC000000700000000 | ((1 << core2_get_pmc_count()) - 1);
> > wrmsrl(MSR_CORE_PERF_GLOBAL_OVF_CTRL, msr_content);
>
> Jan
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