linux-kernel - Re: [PATCH v8 9/9] perf/amd/iommu: Enable support for multiple IOMMUs

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Date:   Tue, 7 Feb 2017 08:57:52 +0700
From:   Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>
To:     Peter Zijlstra <peterz@...radead.org>
CC:     <linux-kernel@...r.kernel.org>, <iommu@...ts.linux-foundation.org>,
        <joro@...tes.org>, <bp@...en8.de>, <mingo@...hat.com>
Subject: Re: [PATCH v8 9/9] perf/amd/iommu: Enable support for multiple IOMMUs

Peter,

On 1/25/17 16:46, Peter Zijlstra wrote:
> On Mon, Jan 16, 2017 at 01:23:36AM -0600, Suravee Suthikulpanit wrote:
>
>> +	pi = container_of(event->pmu, struct perf_amd_iommu, pmu);
>> +	hwc->idx              = pi->idx;
>> +	hwc->config           = event->attr.config;
>> +	hwc->extra_reg.config = event->attr.config1;
>
>>  static void perf_iommu_enable_event(struct perf_event *ev)
>>  {
>> +	struct hw_perf_event *hwc = &ev->hw;
>>  	u8 csource = _GET_CSOURCE(ev);
>>  	u16 devid = _GET_DEVID(ev);
>>  	u8 bank = _GET_BANK(ev);
>> @@ -253,30 +248,34 @@ static void perf_iommu_enable_event(struct perf_event *ev)
>>  	u64 reg = 0ULL;
>>
>>  	reg = csource;
>> -	amd_iommu_pc_set_reg(0, bank, cntr,
>> +	amd_iommu_pc_set_reg(hwc->idx, bank, cntr,
>>  			     IOMMU_PC_COUNTER_SRC_REG, &reg);
>
> Please explain about this IOMMU crud, this looks like fail.
> hwc->idx should be the counter, not a random pmu index.

Ok, I thought this was not used by the code, so I used it for
holding PMU index. This might not be a good idea.
I will change this part per Boris comment in the reply of this
thread.

> But instead it looks like you get the counter form:
>
>   #define _GET_CNTR(ev)       ((u8)(ev->hw.extra_reg.reg))
>
> Which is absolutely insane.
>

So, the IOMMU counters are grouped into bank, and there could be
many banks. I use the extra_reg.reg to hold the bank and counter
indices. This will be used to program onto the counter configuration
register. This is handled in get_next_avail_iommu_bnk_cntr() and
clear_avail_iommu_bnk_cntr().

Thanks,
Suravee