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Wed, 04 Nov 2026 10:49:30 -0800 (PST) Received: from localhost ([2600:1702:7a90:6f9f:66f3:d5d6:2d12:d460]) by smtp.gmail.com with ESMTPSA id 956f58d0204a3-67bee28e4e1sm1983347d50.17.2026.11.04.10.49.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 04 Nov 2026 10:49:29 -0800 (PST) From: Matt Turner Date: Wed, 04 Nov 2026 13:49:19 -0500 Subject: [PATCH v6 12/13] alpha/perf: sample only retired instructions for precise events X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20261104-alpha-profileme-v6-12-63362e9290a3@gmail.com> References: <20261104-alpha-profileme-v6-0-63362e9290a3@gmail.com> In-Reply-To: <20261104-alpha-profileme-v6-0-63362e9290a3@gmail.com> To: Richard Henderson , Magnus Lindholm , Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Namhyung Kim , Mark Rutland , Alexander Shishkin , Jiri Olsa , Ian Rogers , Adrian Hunter , James Clark Cc: linux-alpha@vger.kernel.org, linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, Matt Turner X-Mailer: b4 0.15.2 X-Developer-Signature: v=1; a=openpgp-sha256; l=1874; i=mattst88@gmail.com; h=from:subject:message-id; bh=dXinNQWRSOHUF7W4/7e5c+VGWyfWHZj2yb6aCe5eh9I=; b=kA0DAAoWrOspdAyaTpcByyZiAGrrfiWhrdh1ohcZkL3nl5+bqVxZIQ6Hu94iqr9FHGv6llraq ojxBAAWCgCZFiEEXq8hBJqGuKVMyxv6rOspdAyaTpcFAmrrfiUbFIAAAAAABAAObWFudTIsMi41 KzEuMTIsMiwyXxSAAAAAAC4AKGlzc3Vlci1mcHJAbm90YXRpb25zLm9wZW5wZ3AuZmlmdGhob3J zZW1hbi5uZXQ1RUFGMjEwNDlBODZCOEE1NENDQjFCRkFBQ0VCMjk3NDBDOUE0RTk3AAoJEKzrKX QMmk6XxhgA/0Y0ha3Nl0y6k33nwxDP4L3wVWh6lAWbgaQRyd3mXDqfAQDnDfnx3+h6FfO9gLlXj IESk2GyTMmJxMsvAjrGdXOgCQ== X-Developer-Key: i=mattst88@gmail.com; a=openpgp; fpr=3BB639E56F861FA2E86505690FDD682D974CA72A ProfileMe samples include instructions killed on a wrong path, which show up as hot spots in perf report although they did no work. On an EV7 loop with a randomly mispredicted branch, 19% of the samples were killed before being mapped and another 48% later. PEBS and AMD IBS op samples are of retired instructions only, so make precise_ip imply the retired filter, unless filters are given. The profileme bit still selects every sample. With cycles:p, both kinds of killed sample went to 0%. DTB miss samples, whose instruction is aborted, are then dropped too: cycles:p reports DTB hits only, and the misses need cpu/cycles,trapped/p. The kept samples carry the full period, as do those AMD IBS keeps when its swfilt discards others. So in frequency mode the sample rate, and the event count perf report estimates from the periods, fall by the share of killed instructions: to about a third on that loop. Suggested-by: Ian Rogers Assisted-by: Claude:claude-opus-5-5 Signed-off-by: Matt Turner --- arch/alpha/kernel/perf_event.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/arch/alpha/kernel/perf_event.c b/arch/alpha/kernel/perf_event.c index 32a8b5c98381..7e34eac0ea47 100644 --- a/arch/alpha/kernel/perf_event.c +++ b/arch/alpha/kernel/perf_event.c @@ -837,6 +837,11 @@ static int __hw_perf_event_init(struct perf_event *event) if (attr->config1 && !profileme) return -EINVAL; hwc->config = attr->config1; + /* As with PEBS, precise samples are of retired instructions. */ + if (attr->precise_ip && !attr->config1 && + !(attr->type == PERF_TYPE_RAW && + (attr->config & ALPHA_PERF_CONFIG_PROFILEME))) + hwc->config = ALPHA_PERF_CONFIG1_RETIRED; if (attr->type == PERF_TYPE_RAW && (attr->config & ALPHA_PERF_CONFIG_RANDOMIZE)) { -- 2.55.0