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From: Alexey Budankov <alexey.budankov@linux.intel.com>
To: Andi Kleen <ak@linux.intel.com>
Cc: linux-kernel-owner@vger.kernel.org, peterz@infradead.org,
	tglx@linutronix.de, acme@kernel.org, mingo@redhat.com,
	linux-kernel@vger.kernel.org, jolsa@redhat.com,
	namhyung@kernel.org, Kan Liang <kan.liang@linux.intel.com>
Subject: Re: [PATCH] perf/x86/intel/lbr: Optimize context switches for LBR
Date: Fri, 14 Sep 2018 12:22:36 +0300	[thread overview]
Message-ID: <529b2498-0515-e33c-ebcc-af2a5ca7d974@linux.intel.com> (raw)
In-Reply-To: <20180914085409.GA27886@tassilo.jf.intel.com>


Hi Andi,

On 14.09.2018 11:54, Andi Kleen wrote:
>>> In principle the LBRs need to be flushed between threads. So does
>>> current code.
>>
>> IMHO, ideally, LBRs stack would be preserved and restored when 
>> switching between execution stacks. That would allow implementing 
>> per-thread statistical call graph view in Perf tools, fully based 
>> on HW capabilities. It could be advantageous for some cases, in 
>> comparison with traditional dwarf based call graph. 
> 
> This is already supported when you use LBR call stack mode
> (perf record --call-graph lbr)

Which kernel versions does it make sense to try?

Thanks,
Alexey

> 
> This change is only optimizing the case when call stack mode is not used.
> 
> Of course in call stack mode the context switch overhead is even higher,
> because it not only writes, but also reads.
> 
> -Andi
> 

  reply	other threads:[~2018-09-14  9:23 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-09-13 20:08 [PATCH] perf/x86/intel/lbr: Optimize context switches for LBR kan.liang
2018-09-14  6:47 ` Alexey Budankov
2018-09-14  8:54   ` Andi Kleen
2018-09-14  9:22     ` Alexey Budankov [this message]
2018-09-14 12:39       ` Liang, Kan
2018-09-14 14:27         ` Andi Kleen
2018-09-14 14:57           ` Liang, Kan
2018-09-17  7:57             ` Alexey Budankov

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