linux-kernel - Re: [PATCH v3 3/8] perf: Add a flags parameter to pmu txn interfaces

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Date:	Thu, 16 Jul 2015 22:48:07 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
Cc:	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	linux-s390@...r.kernel.org, sparclinux@...r.kernel.org
Subject: Re: [PATCH v3 3/8] perf: Add a flags parameter to pmu txn interfaces

On Tue, Jul 14, 2015 at 08:01:50PM -0700, Sukadev Bhattiprolu wrote:
> +DEFINE_PER_CPU(int, nop_txn_flags);
> +
> +static int nop_txn_flags_get_and_clear(void)
> +{
> +	int *flagsp;
> +	int flags;
> +	
> +	flagsp = &get_cpu_var(nop_txn_flags);
> +
> +	flags = *flagsp;
> +	*flagsp = 0;
> +
> +	put_cpu_var(nop_txn_flags);
> +
> +	return flags;
> +}
> +
> +static void nop_txn_flags_set(int flags)
> +{
> +	int *flagsp;
> +	
> +	flagsp = &get_cpu_var(nop_txn_flags);
> +	*flagsp = flags;
> +	put_cpu_var(nop_txn_flags);
> +}

That's really horrible, see below:

> +static void perf_pmu_start_txn(struct pmu *pmu, int flags)
>  {
	__this_cpu_write(nop_txn_flags, flags);
> +
> +	if (flags & ~PERF_PMU_TXN_ADD)
> +		return;
> +
>  	perf_pmu_disable(pmu);
>  }
>  
>  static int perf_pmu_commit_txn(struct pmu *pmu)
>  {
	int flags = __this_cpu_read(nop_txn_flags);
	__this_cpu_write(nop_txn_flags, 0);
> +
> +	if (flags & ~PERF_PMU_TXN_ADD)
> +		return 0;
> +
>  	perf_pmu_enable(pmu);
>  	return 0;
>  }
>  
>  static void perf_pmu_cancel_txn(struct pmu *pmu)
>  {
	int flags = __this_cpu_read(nop_txn_flags);
	__this_cpu_write(nop_txn_flags, 0);
> +
> +	if (flags & ~PERF_PMU_TXN_ADD)
> +		return;
> +
>  	perf_pmu_enable(pmu);
>  }
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