Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH V2] perf/x86/intel: Apply mid ACK for small core
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     mingo@redhat.com, linux-kernel@vger.kernel.org, ak@linux.intel.com,
        stable@vger.kernel.org
References: <1627997128-57891-1-git-send-email-kan.liang@linux.intel.com>
 <YQlY2o62E5A9xcdq@hirez.programming.kicks-ass.net>
From:   "Liang, Kan" <kan.liang@linux.intel.com>
Message-ID: <9b0cb4ec-e8b8-3739-7b8d-e1c05785023a@linux.intel.com>
Date:   Tue, 3 Aug 2021 11:20:20 -0400
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101
 Thunderbird/78.12.0
MIME-Version: 1.0
In-Reply-To: <YQlY2o62E5A9xcdq@hirez.programming.kicks-ass.net>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Precedence: bulk


On 8/3/2021 10:55 AM, Peter Zijlstra wrote:
> On Tue, Aug 03, 2021 at 06:25:28AM -0700, kan.liang@linux.intel.com wrote:
>> From: Kan Liang <kan.liang@linux.intel.com>
>>
>> A warning as below may be occasionally triggered in an ADL machine when
>> these conditions occur,
>> - Two perf record commands run one by one. Both record a PEBS event.
>> - Both runs on small cores.
>> - They have different adaptive PEBS configuration (PEBS_DATA_CFG).
>>
>> [  673.663291] WARNING: CPU: 4 PID: 9874 at
>> arch/x86/events/intel/ds.c:1743
>> setup_pebs_adaptive_sample_data+0x55e/0x5b0
>> [  673.663348] RIP: 0010:setup_pebs_adaptive_sample_data+0x55e/0x5b0
>> [  673.663357] Call Trace:
>> [  673.663357]  <NMI>
>> [  673.663357]  intel_pmu_drain_pebs_icl+0x48b/0x810
>> [  673.663360]  perf_event_nmi_handler+0x41/0x80
>> [  673.663368]  </NMI>
>> [  673.663370]  __perf_event_task_sched_in+0x2c2/0x3a0
>>
>> Different from the big core, the small core requires the ACK right
>> before re-enabling counters in the NMI handler, otherwise a stale PEBS
>> record may be dumped into the later NMI handler, which trigger the
>> warning.
>>
>> Add a new mid_ack flag to track the case. Add all PMI handler bits in
>> the struct x86_hybrid_pmu to track the bits for different types of PMUs.
>> Apply mid ACK for the small cores on an Alder Lake machine.
> 
> Why do we need a new option? Why isn't early (as in not late) good
> enough?
> 

The early ACK can fix this issue, however it triggers a spurious NMI 
during the stress test. I'm told to do the ACK right before re-enabling 
counters for small cores. That indeed fixes all the issues.

Thanks,
Kan