linux-kernel - Re: [PATCH 2/4] x86 mmiotrace: fix relay-buffer-full flag for SMP

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Date:	Tue, 05 Feb 2008 21:44:07 +0100
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Pekka Paalanen <pq@....fi>
CC:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] x86 mmiotrace: fix relay-buffer-full flag for SMP

Pekka Paalanen a écrit :
> Relay has per-cpu buffers, but mmiotrace was using only a single flag
> for detecting buffer full/not-full transitions. The new code makes
> this per-cpu and actually counts missed events.
> 
> Signed-off-by: Pekka Paalanen <pq@....fi>
> ---
>  arch/x86/kernel/mmiotrace/mmio-mod.c |   26 ++++++++++++++++----------
>  1 files changed, 16 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/x86/kernel/mmiotrace/mmio-mod.c b/arch/x86/kernel/mmiotrace/mmio-mod.c
> index 82ae920..f492b65 100644
> --- a/arch/x86/kernel/mmiotrace/mmio-mod.c
> +++ b/arch/x86/kernel/mmiotrace/mmio-mod.c
> @@ -29,6 +29,7 @@
>  #include <asm/pgtable.h>
>  #include <linux/mmiotrace.h>
>  #include <asm/e820.h> /* for ISA_START_ADDRESS */
> +#include <asm/atomic.h>
>  
>  #include "kmmio.h"
>  #include "pf_in.h"
> @@ -47,9 +48,13 @@ struct trap_reason {
>  	int active_traces;
>  };
>  
> +/* Accessed per-cpu. */
>  static struct trap_reason pf_reason[NR_CPUS];
>  static struct mm_io_header_rw cpu_trace[NR_CPUS];
>  
> +/* Access to this is not per-cpu. */
> +static atomic_t dropped[NR_CPUS];
> +

Please dont introduce NR_CPUS new arrays, since people are working hard to zap 
them from kernel.

You probably can use a per_cpu variable ?

Thank you

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