From: "Liang, Kan" <kan.liang@linux.intel.com>
To: Alexey Budankov <alexey.budankov@linux.intel.com>,
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
Subject: Re: [PATCH] perf/x86/intel/lbr: Optimize context switches for LBR
Date: Fri, 14 Sep 2018 08:39:36 -0400 [thread overview]
Message-ID: <b82d59b2-71bf-2c91-869c-0068760c9ed3@linux.intel.com> (raw)
In-Reply-To: <529b2498-0515-e33c-ebcc-af2a5ca7d974@linux.intel.com>
On 9/14/2018 5:22 AM, Alexey Budankov wrote:
>
> 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?
>
The optimization for LBR call stack has been merged into 4.19.
commit id: 8b077e4a69bef5c4121426e99497975860191e53
perf/x86/intel/lbr: Optimize context switches for the LBR call stack
Thanks,
Kan
> 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
>>
next prev parent reply other threads:[~2018-09-14 12:39 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
2018-09-14 12:39 ` Liang, Kan [this message]
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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