linux-kernel - Re: [PATCH v8 3/9] perf/amd/iommu: Misc fix up perf_iommu

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Date:   Thu, 19 Jan 2017 11:01:48 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>
Cc:     linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
        joro@...tes.org, peterz@...radead.org, mingo@...hat.com
Subject: Re: [PATCH v8 3/9] perf/amd/iommu: Misc fix up perf_iommu_read

> Subject: Re: [PATCH v8 3/9] perf/amd/iommu: Misc fix up perf_iommu_read

Please be a bit more thorough when writing your commit messages. What is
a "misc fix up"? Perhaps it is ok for a quick'n'dirty local patch but
not when it is for upstream.

Also, function names end with "()" to denote they're functions.

On Mon, Jan 16, 2017 at 01:23:30AM -0600, Suravee Suthikulpanit wrote:
> * Fix overflow handling since u64 delta would lose the MSB sign bit.
> * Remove unnecessary local64_cmpxchg().
> * Coding style and make use of GENMASK_ULL macro.

That last one doesn't read like a sentence.

> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Borislav Petkov <bp@...en8.de>
> Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
> ---
>  arch/x86/events/amd/iommu.c | 23 ++++++++++++-----------
>  1 file changed, 12 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/x86/events/amd/iommu.c b/arch/x86/events/amd/iommu.c
> index 1aa25d8..3f1c18a 100644
> --- a/arch/x86/events/amd/iommu.c
> +++ b/arch/x86/events/amd/iommu.c
> @@ -320,9 +320,8 @@ static void perf_iommu_start(struct perf_event *event, int flags)
>  
>  static void perf_iommu_read(struct perf_event *event)
>  {
> -	u64 count = 0ULL;
> -	u64 prev_raw_count = 0ULL;
> -	u64 delta = 0ULL;
> +	u64 count, prev;
> +	s64 delta;
>  	struct hw_perf_event *hwc = &event->hw;
>  
>  	amd_iommu_pc_get_set_reg_val(_GET_DEVID(event),
> @@ -330,18 +329,20 @@ static void perf_iommu_read(struct perf_event *event)
>  				IOMMU_PC_COUNTER_REG, &count, false);
>  
>  	/* IOMMU pc counter register is only 48 bits */
> -	count &= 0xFFFFFFFFFFFFULL;
> +	count &= GENMASK_ULL(48, 0);

GENMASK_ULL(48, 0) gives 0x1ffffffffffff, however. Which is 49 bits.

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.