linux-kernel - Re: [PATCH v2] perf: Rewrite core context handling

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Date:   Tue, 11 Oct 2022 18:49:55 +0530
From:   Ravi Bangoria <ravi.bangoria@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     acme@...nel.org, alexander.shishkin@...ux.intel.com,
        jolsa@...hat.com, namhyung@...nel.org, songliubraving@...com,
        eranian@...gle.com, ak@...ux.intel.com, mark.rutland@....com,
        frederic@...nel.org, maddy@...ux.ibm.com, irogers@...gle.com,
        will@...nel.org, robh@...nel.org, mingo@...hat.com,
        catalin.marinas@....com, ndesaulniers@...gle.com,
        srw@...dewatkins.net, linux-arm-kernel@...ts.infradead.org,
        linux-perf-users@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        sandipan.das@....com, ananth.narayan@....com, kim.phillips@....com,
        santosh.shukla@....com, Ravi Bangoria <ravi.bangoria@....com>
Subject: Re: [PATCH v2] perf: Rewrite core context handling

On 11-Oct-22 4:59 PM, Peter Zijlstra wrote:
> On Sat, Oct 08, 2022 at 11:54:24AM +0530, Ravi Bangoria wrote:
> 
>> +static void perf_event_swap_task_ctx_data(struct perf_event_context *prev_ctx,
>> +					  struct perf_event_context *next_ctx)
>> +{
>> +	struct perf_event_pmu_context *prev_epc, *next_epc;
>> +
>> +	if (!prev_ctx->nr_task_data)
>> +		return;
>> +
>> +	prev_epc = list_first_entry(&prev_ctx->pmu_ctx_list,
>> +				    struct perf_event_pmu_context,
>> +				    pmu_ctx_entry);
>> +	next_epc = list_first_entry(&next_ctx->pmu_ctx_list,
>> +				    struct perf_event_pmu_context,
>> +				    pmu_ctx_entry);
>> +
>> +	while (&prev_epc->pmu_ctx_entry != &prev_ctx->pmu_ctx_list &&
>> +	       &next_epc->pmu_ctx_entry != &next_ctx->pmu_ctx_list) {
>> +
>> +		WARN_ON_ONCE(prev_epc->pmu != next_epc->pmu);
>> +
>> +		/*
>> +		 * PMU specific parts of task perf context can require
>> +		 * additional synchronization. As an example of such
>> +		 * synchronization see implementation details of Intel
>> +		 * LBR call stack data profiling;
>> +		 */
>> +		if (prev_epc->pmu->swap_task_ctx)
>> +			prev_epc->pmu->swap_task_ctx(prev_epc, next_epc);
>> +		else
>> +			swap(prev_epc->task_ctx_data, next_epc->task_ctx_data);
> 
> Did I forget to advance the iterators here?

Yeah. Seems so. I overlooked it too.

Thanks,
Ravi