linux-kernel - Re: [PATCH 06/13] perf/x86/amd: Support PERF_SAMPLE_PHY_ADDR using IBS_DC

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Message-ID: <20220526110947.GQ2578@worktop.programming.kicks-ass.net>
Date:   Thu, 26 May 2022 13:09:47 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Ravi Bangoria <ravi.bangoria@....com>
Cc:     acme@...nel.org, jolsa@...nel.org, namhyung@...nel.org,
        eranian@...gle.com, irogers@...gle.com, jmario@...hat.com,
        leo.yan@...aro.org, alisaidi@...zon.com, ak@...ux.intel.com,
        kan.liang@...ux.intel.com, dave.hansen@...ux.intel.com,
        hpa@...or.com, mingo@...hat.com, mark.rutland@....com,
        alexander.shishkin@...ux.intel.com, tglx@...utronix.de,
        bp@...en8.de, x86@...nel.org, linux-perf-users@...r.kernel.org,
        linux-kernel@...r.kernel.org, sandipan.das@....com,
        ananth.narayan@....com, kim.phillips@....com,
        santosh.shukla@....com
Subject: Re: [PATCH 06/13] perf/x86/amd: Support PERF_SAMPLE_PHY_ADDR using
 IBS_DC_PHYSADDR

On Thu, May 26, 2022 at 04:29:22PM +0530, Ravi Bangoria wrote:
> On 26-May-22 3:26 PM, Peter Zijlstra wrote:
> > On Thu, May 26, 2022 at 02:16:28PM +0530, Ravi Bangoria wrote:
> >> On 25-May-22 4:51 PM, Peter Zijlstra wrote:
> >>> On Wed, May 25, 2022 at 03:09:31PM +0530, Ravi Bangoria wrote:
> >>>> IBS_DC_PHYSADDR provides the physical data address for the tagged load/
> >>>> store operation. Populate perf sample physical address using it.
> >>>>
> >>>> Signed-off-by: Ravi Bangoria <ravi.bangoria@....com>
> >>>> ---
> >>>>  arch/x86/events/amd/ibs.c | 26 +++++++++++++++++++++++++-
> >>>>  1 file changed, 25 insertions(+), 1 deletion(-)
> >>>>
> >>>> diff --git a/arch/x86/events/amd/ibs.c b/arch/x86/events/amd/ibs.c
> >>>> index b57736357e25..c719020c0e83 100644
> >>>> --- a/arch/x86/events/amd/ibs.c
> >>>> +++ b/arch/x86/events/amd/ibs.c
> >>>> @@ -986,13 +986,35 @@ static void perf_ibs_get_data_addr(struct perf_event *event,
> >>>>  	data->addr = ibs_data->regs[ibs_op_msr_idx(MSR_AMD64_IBSDCLINAD)];
> >>>>  }
> >>>>  
> >>>> +static void perf_ibs_get_phy_addr(struct perf_event *event,
> >>>> +				  struct perf_ibs_data *ibs_data,
> >>>> +				  struct perf_sample_data *data)
> >>>> +{
> >>>> +	union perf_mem_data_src *data_src = &data->data_src;
> >>>> +	u64 op_data3 = ibs_data->regs[ibs_op_msr_idx(MSR_AMD64_IBSOPDATA3)];
> >>>> +	u64 phy_addr_valid = op_data3 & IBS_DC_PHY_ADDR_VALID_MASK;
> >>>> +
> >>>> +	if (!(event->attr.sample_type & PERF_SAMPLE_DATA_SRC))
> >>>> +		perf_ibs_get_mem_op(op_data3, data);
> >>>> +
> >>>> +	if ((data_src->mem_op != PERF_MEM_OP_LOAD &&
> >>>> +	    data_src->mem_op != PERF_MEM_OP_STORE) ||
> >>>> +	    !phy_addr_valid) {
> >>>> +		data->phys_addr = 0x0;
> >>>> +		return;
> >>>> +	}
> >>>> +
> >>>> +	data->phys_addr = ibs_data->regs[ibs_op_msr_idx(MSR_AMD64_IBSDCPHYSAD)];
> >>>> +}
> >>>
> >>> perf_prepare_sample() will unconditionally overwrite data->phys_addr.
> >>> There is currently no facility to let the driver set this field.
> >>
> >> Thanks for pointing it Peter. Would you mind if I add:
> > 
> > I think it's best if you extend/mimic the __PERF_SAMPLE_CALLCHAIN_EARLY
> > hack. It's more or less the same problem and then at least the solution
> > is consistent.
> 
> I've one more identical optimization in my list. IBS_OP_DATA3[IbsDcPgSz]
> can provide PERF_SAMPLE_DATA_PAGE_SIZE. I hope consuming two more bits
> for internal purpose is okay.

Yeah, I suppose so.. we'll need to hunt for bits once we run out, but
that's how it is...