linux-kernel - Re: [PATCH] perf pmu: Create x86 specific perf_pmu__valid

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Date:   Tue, 20 Jul 2021 09:56:57 +0100
From:   John Garry <john.garry@...wei.com>
To:     Jin Yao <yao.jin@...ux.intel.com>, <acme@...nel.org>,
        <jolsa@...nel.org>, <peterz@...radead.org>, <mingo@...hat.com>,
        <alexander.shishkin@...ux.intel.com>
CC:     <Linux-kernel@...r.kernel.org>, <linux-perf-users@...r.kernel.org>,
        <ak@...ux.intel.com>, <kan.liang@...el.com>, <yao.jin@...el.com>
Subject: Re: [PATCH] perf pmu: Create x86 specific perf_pmu__valid_suffix

On 20/07/2021 09:20, Jin Yao wrote:
> The commit c47a5599eda3 ("perf tools: Fix pattern matching for same
> substring in different PMU type") breaks arm64 system because it
> assumes the first token must be followed by a '_', but it is
> possibly a numeric on arm64.

I wouldn't just say arm64. The core code should support matching 
multiple tokens, but it just so happens that only arm64 uses it.

> 
> For example, perf_pmu__valid_suffix("hisi_sccl3_l3c7", "hisi_sccl")
> fails. "hisi_sccl3_l3c7" is pmu name and "hisi_sccl" is token.
> "hisi_sccl" is followed by a digit but not followed by a '_'
> ('3' in this example).
> 
> Since the PMU alias format on arm64 has difference than the format
> on x86. Create a x86 specific perf_pmu__valid_suffix. For other arch,
> the weak function always returns true to keep original behavior
> unchanged.
> 
> Fixes: c47a5599eda3 ("perf tools: Fix pattern matching for same substring in different PMU type")
> Signed-off-by: Jin Yao<yao.jin@...ux.intel.com>
> Reported-by: John Garry<john.garry@...wei.com>
> ---

I tend not to agree with this solution. Let's not make it x86 vs non-x86 
problem. Indeed, if we continue to support custom PMU alias matching 
per-arch, then it becomes a maintenance burden.

So this change fixes my initial problem:

-----8<------

 From bbc9c7bf65c9cea756f0716dd717e9cfc767ba39 Mon Sep 17 00:00:00 2001
From: John Garry <john.garry@...wei.com>
Date: Tue, 20 Jul 2021 09:48:22 +0100
Subject: [PATCH] perf pmu: Only check valid suffix for final token

Since commit 730670b1d108 ("perf pmu: Support more complex PMU event
aliasing"), matching multiple alias tokens has been supported.

However, commit c47a5599eda32 ("perf tools: Fix pattern matching for 
same substring in different PMU type"), ignored the possibility of 
multiple tokens, and assumed that we can only match on valid suffix and 
a single token.

Fix multiple token support by only checking valid suffix from final token.

diff --git a/tools/perf/util/pmu.c b/tools/perf/util/pmu.c
index 44b90d638ad5..6de2275b2ae2 100644
--- a/tools/perf/util/pmu.c
+++ b/tools/perf/util/pmu.c
@@ -789,12 +789,17 @@ bool pmu_uncore_alias_match(const char *pmu_name, 
const char *name)
  	 *	    match "socket" in "socketX_pmunameY" and then "pmuname" in
  	 *	    "pmunameY".
  	 */
-	for (; tok; name += strlen(tok), tok = strtok_r(NULL, ",", &tmp)) {
+	for (; ; ) {
+		char *next_tok = strtok_r(NULL, ",", &tmp);
  		name = strstr(name, tok);
-		if (!name || !perf_pmu__valid_suffix((char *)name, tok)) {
+		if (!name || (!perf_pmu__valid_suffix((char *)name, tok) && !next_tok)) {
  			res = false;
  			goto out;
  		}
+		if (!next_tok)
+			break;
+		name += strlen(tok);
+		tok = next_tok;
  	}

  	res = true;
-- 
2.26.2

----->8------

Please check it.

I need to check the other place perf_pmu__valid_suffix() is referenced 
(perf_pmu__match()) to see if anything is broken there.

Thanks,
John