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From: "Liang, Kan" <kan.liang@linux.intel.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: acme@kernel.org, mingo@redhat.com, linux-kernel@vger.kernel.org,
	tglx@linutronix.de, jolsa@kernel.org, eranian@google.com,
	alexander.shishkin@linux.intel.com, ak@linux.intel.com
Subject: Re: [PATCH 4/9] perf/x86/intel: Support hardware TopDown metrics
Date: Wed, 29 May 2019 10:42:29 -0400	[thread overview]
Message-ID: <09770caf-e717-5b11-d11f-f30cb027bb05@linux.intel.com> (raw)
In-Reply-To: <20190529075720.GB2623@hirez.programming.kicks-ass.net>



On 5/29/2019 3:57 AM, Peter Zijlstra wrote:
> On Tue, May 28, 2019 at 02:24:56PM -0400, Liang, Kan wrote:
>>
>>
>> On 5/28/2019 9:48 AM, Peter Zijlstra wrote:
>>> On Tue, May 21, 2019 at 02:40:50PM -0700, kan.liang@linux.intel.com wrote:
>>>> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
>>>> index b980b9e95d2a..0d7081434d1d 100644
>>>> --- a/include/linux/perf_event.h
>>>> +++ b/include/linux/perf_event.h
>>>> @@ -133,6 +133,11 @@ struct hw_perf_event {
>>>>    			struct hw_perf_event_extra extra_reg;
>>>>    			struct hw_perf_event_extra branch_reg;
>>>> +
>>>> +			u64		saved_metric;
>>>> +			u64		saved_slots;
>>>> +			u64		last_slots;
>>>> +			u64		last_metric;
>>>
>>> This is really sad, and I'm thinking much of that really isn't needed
>>> anyway, due to how you're not using some of the other fields.
>>
>> If we don't cache the value, we have to update all metrics events when
>> reading any metrics event. I think that could bring high overhead.
> 
> Since you don't support sampling, or even 'normal' functionality on this
> FIXED3/SLOTS thing, you'll not use prev_count, sample_period,
> last_period, period_left, interrupts_seq, interrupts, freq_time_stamp
> and freq_count_stamp.
> 
> So why do you then need to grow the data structure with 4 more nonsense
> fields?
> 
> Also, I'm not sure what you need those last things for, you reset the
> value to 0 every time you read them, there is no delta to track.
> 

The 'last things' are only for per-thread Topdown RDPMC.
We have to save/restore slots and metrics value in context switch.
It's used to calculate the delta between thread shced in and current 
read/sched out.


I will split the patch into several patches, and try to make things clear.

Thanks,
Kan



  reply	other threads:[~2019-05-29 14:42 UTC|newest]

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-21 21:40 [PATCH 0/9] TopDown metrics support for Icelake kan.liang
2019-05-21 21:40 ` [PATCH 1/9] perf/core: Support a REMOVE transaction kan.liang
2019-05-21 21:40 ` [PATCH 2/9] perf/x86/intel: Basic support for metrics counters kan.liang
2019-05-28 12:05   ` Peter Zijlstra
2019-05-28 18:20     ` Liang, Kan
2019-05-28 12:15   ` Peter Zijlstra
2019-05-28 18:21     ` Liang, Kan
2019-05-29  7:28       ` Peter Zijlstra
2019-05-29 14:40         ` Liang, Kan
2019-05-29 16:46           ` Peter Zijlstra
2019-05-29  8:14   ` Peter Zijlstra
2019-05-21 21:40 ` [PATCH 3/9] perf/x86/intel: Support overflows on SLOTS kan.liang
2019-05-28 12:20   ` Peter Zijlstra
2019-05-28 18:22     ` Liang, Kan
2019-05-21 21:40 ` [PATCH 4/9] perf/x86/intel: Support hardware TopDown metrics kan.liang
2019-05-28 12:43   ` Peter Zijlstra
2019-05-28 18:23     ` Liang, Kan
2019-05-29  7:30       ` Peter Zijlstra
2019-05-28 12:53   ` Peter Zijlstra
2019-05-28 12:56   ` Peter Zijlstra
2019-05-28 13:32     ` Peter Zijlstra
2019-05-28 13:30   ` Peter Zijlstra
2019-05-28 18:24     ` Liang, Kan
2019-05-29  7:34       ` Peter Zijlstra
2019-05-29 14:41         ` Liang, Kan
2019-05-28 13:43   ` Peter Zijlstra
2019-05-28 18:24     ` Liang, Kan
2019-05-29  7:54       ` Peter Zijlstra
2019-05-29 14:42         ` Liang, Kan
2019-05-29 16:58           ` Peter Zijlstra
2019-06-04 20:39             ` Liang, Kan
2019-05-28 13:48   ` Peter Zijlstra
2019-05-28 18:24     ` Liang, Kan
2019-05-29  7:57       ` Peter Zijlstra
2019-05-29 14:42         ` Liang, Kan [this message]
2019-05-21 21:40 ` [PATCH 5/9] perf/x86/intel: Set correct weight for TopDown metrics events kan.liang
2019-05-28 13:50   ` Peter Zijlstra
2019-05-21 21:40 ` [PATCH 6/9] perf/x86/intel: Export new TopDown metrics events for Icelake kan.liang
2019-05-21 21:40 ` [PATCH 7/9] perf/x86/intel: Disable sampling read slots and topdown kan.liang
2019-05-28 13:52   ` Peter Zijlstra
2019-05-28 18:25     ` Liang, Kan
2019-05-29  7:58       ` Peter Zijlstra
2019-05-21 21:40 ` [PATCH 8/9] perf, tools, stat: Support new per thread TopDown metrics kan.liang
2019-05-21 21:40 ` [PATCH 9/9] perf, tools: Add documentation for topdown metrics kan.liang

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