linux-kernel - Re: [PATCH v2 3/7] arch/x86/amd/ibs: Fix re-arming IBS Fetch

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Message-ID: <f44ffa72-815e-925d-101c-c096a3879990@amd.com>
Date:   Thu, 10 Sep 2020 10:58:58 -0500
From:   Kim Phillips <kim.phillips@....com>
To:     peterz@...radead.org
Cc:     Borislav Petkov <bp@...en8.de>, Borislav Petkov <bp@...e.de>,
        Ingo Molnar <mingo@...nel.org>, Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Stephane Eranian <eranian@...gle.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>, Jiri Olsa <jolsa@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Michael Petlan <mpetlan@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>,
        Stephane Eranian <stephane.eranian@...gle.com>,
        stable@...r.kernel.org
Subject: Re: [PATCH v2 3/7] arch/x86/amd/ibs: Fix re-arming IBS Fetch

On 9/10/20 3:50 AM, peterz@...radead.org wrote:
> On Thu, Sep 10, 2020 at 10:32:23AM +0200, peterz@...radead.org wrote:
>>> @@ -363,7 +363,14 @@ perf_ibs_event_update(struct perf_ibs *perf_ibs, struct perf_event *event,
>>>  static inline void perf_ibs_enable_event(struct perf_ibs *perf_ibs,
>>>  					 struct hw_perf_event *hwc, u64 config)
>>>  {
>>> -	wrmsrl(hwc->config_base, hwc->config | config | perf_ibs->enable_mask);
>>> +	u64 _config = (hwc->config | config) & ~perf_ibs->enable_mask;
>>> +
>>> +	/* On Fam17h, the periodic fetch counter is set when IbsFetchEn is changed from 0 to 1 */
>>> +	if (perf_ibs == &perf_ibs_fetch && boot_cpu_data.x86 >= 0x16 && boot_cpu_data.x86 <= 0x18)
>>> +		wrmsrl(hwc->config_base, _config);
> 
>> A better option would be to use hwc->flags, you're loading from that
>> line already, so it's guaranteed hot and then you only have a single
>> branch. Or stick it in perf_ibs near enable_mask, same difference.
> 
> I fixed it for you.

> @@ -370,7 +371,13 @@ perf_ibs_event_update(struct perf_ibs *p
>  static inline void perf_ibs_enable_event(struct perf_ibs *perf_ibs,
>  					 struct hw_perf_event *hwc, u64 config)
>  {
> -	wrmsrl(hwc->config_base, hwc->config | config | perf_ibs->enable_mask);
> +	u64 _config = (hwc->config | config) & ~perf_ibs->enable_mask;
> +
> +	if (perf_ibs->fetch_count_reset_broken)

Nice, we don't even need the perf_ibs == &perf_ibs_fetch check
here because fetch_count_reset_broken is guaranteed to be 0 in
perf_ibs_op.

Thanks!

Kim