linux-kernel - Re: [PATCH 4/9] perf/x86: add cross-HT counter exclusion infrastructure

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Date:	Thu, 5 Jun 2014 09:47:53 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, ak@...ux.intel.com,
	jolsa@...hat.com, zheng.z.yan@...el.com,
	maria.n.dimakopoulou@...il.com
Subject: Re: [PATCH 4/9] perf/x86: add cross-HT counter exclusion
 infrastructure

On Wed, Jun 04, 2014 at 11:34:13PM +0200, Stephane Eranian wrote:
> From: Maria Dimakopoulou <maria.n.dimakopoulou@...il.com>
> 
> This patch adds a new shared_regs style structure to the
> per-cpu x86 state (cpuc). It is used to coordinate access
> between counters which must be used with exclusion across
> HyperThreads on Intel processors. This new struct is not
> needed on each PMU, thus is is allocated on demand.
> 
> Reviewed-by: Stephane Eranian <eranian@...gle.com>
> Signed-off-by: Maria Dimakopoulou <maria.n.dimakopoulou@...il.com>
> ---
>  arch/x86/kernel/cpu/perf_event.h       |   40 ++++++++++++++++++--
>  arch/x86/kernel/cpu/perf_event_intel.c |   63 +++++++++++++++++++++++++++++---
>  2 files changed, 94 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/perf_event.h b/arch/x86/kernel/cpu/perf_event.h
> index 413799f..5da0a2b 100644
> --- a/arch/x86/kernel/cpu/perf_event.h
> +++ b/arch/x86/kernel/cpu/perf_event.h
> @@ -65,10 +65,11 @@ struct event_constraint {
>  /*
>   * struct hw_perf_event.flags flags
>   */
> -#define PERF_X86_EVENT_PEBS_LDLAT	0x1 /* ld+ldlat data address sampling */
> -#define PERF_X86_EVENT_PEBS_ST		0x2 /* st data address sampling */
> -#define PERF_X86_EVENT_PEBS_ST_HSW	0x4 /* haswell style st data sampling */
> -#define PERF_X86_EVENT_COMMITTED	0x8 /* event passed commit_txn */
> +#define PERF_X86_EVENT_PEBS_LDLAT	0x01 /* ld+ldlat data address sampling */
> +#define PERF_X86_EVENT_PEBS_ST		0x02 /* st data address sampling */
> +#define PERF_X86_EVENT_PEBS_ST_HSW	0x04 /* haswell style st data sampling */
> +#define PERF_X86_EVENT_COMMITTED	0x08 /* event passed commit_txn */
> +#define PERF_X86_EVENT_EXCL		0x10 /* HT exclusivity on counter */
>  
>  struct amd_nb {
>  	int nb_id;  /* NorthBridge id */
> @@ -119,6 +120,27 @@ struct intel_shared_regs {
>  	unsigned                core_id;	/* per-core: core id */
>  };
>  
> +enum intel_excl_state_type {
> +	INTEL_EXCL_UNUSED    = 0, /* counter is unused */
> +	INTEL_EXCL_SHARED    = 1, /* counter can be used by both threads */
> +	INTEL_EXCL_EXCLUSIVE = 2, /* counter can be used by one thread only */
> +};
> +
> +struct intel_excl_states {
> +	enum intel_excl_state_type init_state[X86_PMC_IDX_MAX];
> +	enum intel_excl_state_type state[X86_PMC_IDX_MAX];
> +};
> +
> +struct intel_excl_cntrs {
> +	spinlock_t	lock;
> +	unsigned long	lock_flags;
> +
> +	struct intel_excl_states states[2];
> +
> +	int		refcnt;		/* per-core: #HT threads */
> +	unsigned	core_id;	/* per-core: core id */
> +};

This must be a raw_spin_lock_t, its taken from pmu::add() which is
called under perf_event_context::lock, which is raw_spinlock_t, as its
taken under rq::lock, which too is raw_spinlock_t.

I should really get around to fixing these errors and include the
lockdep infrastructure for this.

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