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Tue, 10 Nov 2026 22:54:11 -0800 (PST) Received: from thinkpad.tail59a646.ts.net ([112.199.224.229]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-3751dae6377sm11879272eec.3.2026.11.10.22.54.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 10 Nov 2026 22:54:10 -0800 (PST) From: Hang Zhengyang To: Zhao Gongyi Cc: peterz@infradead.org, mingo@redhat.com, acme@kernel.org, namhyung@kernel.org, mark.rutland@arm.com, alexander.shishkin@linux.intel.com, jolsa@kernel.org, irogers@google.com, adrian.hunter@intel.com, james.clark@linaro.org, tglx@kernel.org, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] perf/x86/amd: Avoid double-decrementing n_pair on failed transactions Date: Wed, 11 Nov 2026 14:54:03 +0800 Message-ID: <20261111065404.3428684-1-hang.zhengyang1010@gmail.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261109111909.31712-1-zhaogongyi@bytedance.com> References: <20261109111909.31712-1-zhaogongyi@bytedance.com> 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-Transfer-Encoding: 8bit On Mon, 9 Nov 2026 19:19:09 +0800, Zhao Gongyi wrote: > On a failed PERF_PMU_TXN_ADD commit, x86_schedule_events() releases > constraints for newly added pair events. The AMD put callback decrements > n_pair, and x86_pmu_cancel_txn() then subtracts n_txn_pair for the same > events. Reproduced in a KVM guest on a Zen 3 host (Ryzen 7 PRO 5850U), kernel 7.3-rc6, with a trace_printk() in x86_schedule_events() and x86_pmu_cancel_txn(). With four pinned cycles events on CPU 0, each failed attempt to add a pinned '{fp_ret_sse_avx_ops.all,cycles}' group leaves n_pair one lower: -1, -2, -3, so gpmax goes 5, 6, 7 on 6 counters. With this patch n_pair is back to 0 after each attempt and gpmax stays 5. Tested-by: Hang Zhengyang To reproduce: perf stat -C 0 -e '{cycles,cycles,cycles,cycles}:D' -- sleep 4 & # three times: perf stat -C 0 -e '{fp_ret_sse_avx_ops.all,cycles}:D' -- taskset -c 0 (Analysis and testing done with an AI assistant; I reproduced the n_pair drift.)