linux-kernel - Re: [PATCH] perf/x86/amd: Do not WARN on every IRQ

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Message-ID: <b1cf5990-1019-49ea-a1e8-e22410922801@amd.com>
Date:   Thu, 14 Sep 2023 16:52:13 +0530
From:   Sandipan Das <sandipan.das@....com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Breno Leitao <leitao@...ian.org>
Cc:     Jirka Hladky <jhladky@...hat.com>, Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Ian Rogers <irogers@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, leit@...com,
        dcostantino@...a.com,
        "open list:PERFORMANCE EVENTS SUBSYSTEM" 
        <linux-perf-users@...r.kernel.org>,
        "open list:PERFORMANCE EVENTS SUBSYSTEM" 
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] perf/x86/amd: Do not WARN on every IRQ

On 9/14/2023 4:48 PM, Peter Zijlstra wrote:
> On Thu, Sep 14, 2023 at 02:30:43AM -0700, Breno Leitao wrote:
>> On Thu, Sep 14, 2023 at 11:12:34AM +0200, Peter Zijlstra wrote:
>>> On Thu, Sep 14, 2023 at 02:25:40PM +0530, Sandipan Das wrote:
>>
>>>> I agree with using WARN_ON_ONCE() to make this less intrusive.
>>>
>>> Could you send a patch that AMD is happy with?
>>
>> Why the current patch is not good enough?
> 
> Sandipan, can you answer this? I don't tihnk I'm qualified to speak for
> the AMD pmu and certainly I don't have insight into their design future.

Hi Breno,

Functionally, the patch looks good to me and I will be reusing it
without any change to the authorship. However, as Peter suggested, I
wanted to add a message to prompt users to update the microcode and
also call out the required patch levels in the commit message since
different Zen 4 variants and steppings use different microcode.

Here's what I plan to send.

diff --git a/arch/x86/events/amd/core.c b/arch/x86/events/amd/core.c
index abadd5f23425..186a124bb3c0 100644
--- a/arch/x86/events/amd/core.c
+++ b/arch/x86/events/amd/core.c
@@ -909,6 +909,13 @@ static int amd_pmu_v2_handle_irq(struct pt_regs *regs)
                status &= ~GLOBAL_STATUS_LBRS_FROZEN;
        }

+       if (status & ~amd_pmu_global_cntr_mask)
+               pr_warn_once("Unknown status bits are set (0x%llx), please consider updating microcode\n",
+                            status);
+
+       /* Clear any reserved bits set by buggy microcode */
+       status &= amd_pmu_global_cntr_mask;
+
        for (idx = 0; idx < x86_pmu.num_counters; idx++) {
                if (!test_bit(idx, cpuc->active_mask))
                        continue;

--

Hi Peter,

There is another case where users will see warnings but the patch
to fix it (link below) is yet to be reviewed. May I rebase and
resend it along with the above?

https://lore.kernel.org/all/20230613105809.524535-1-sandipan.das@amd.com/