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b=YqpMQ+cUwMoS+5aLpa0Zc7F87P6hldc2YCxjLq8JJQEut07LwxMgWsZukh3XPOaQ+Dq7na9tUNbpyaZGlbj97OGtETMJVjMjp51V9TDB9VEe7aXgvZUrtU+7W4WAjNLklHsLICRd08V5SaZ//B5hXaXk7QRUUS2KG2VmmC/tvAA= Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=amd.com; Received: from PH7PR12MB5712.namprd12.prod.outlook.com (2603:10b6:510:1e3::13) by IA1PR12MB8519.namprd12.prod.outlook.com (2603:10b6:208:44c::22) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.451.13; Wed, 23 Sep 2026 10:38:55 +0000 Received: from PH7PR12MB5712.namprd12.prod.outlook.com ([fe80::afe1:7dd0:ea71:b7e7]) by PH7PR12MB5712.namprd12.prod.outlook.com ([fe80::afe1:7dd0:ea71:b7e7%4]) with mapi id 15.21.0451.014; Wed, 23 Sep 2026 10:38:55 +0000 Message-ID: <1486211b-1182-4277-b273-bdc84f6d23d7@amd.com> Date: Wed, 23 Sep 2026 16:08:45 +0530 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 0/2] perf/x86/amd/uncore: Drop redundant counter slot searches To: Usama Arif , acme@kernel.org, adrian.hunter@intel.com, alexander.shishkin@linux.intel.com, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, irogers@google.com, james.clark@linaro.org, jolsa@kernel.org, linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, mark.rutland@arm.com, mingo@redhat.com, namhyung@kernel.org, peterz@infradead.org, tglx@kernel.org, x86@kernel.org Cc: hannes@cmpxchg.org, riel@surriel.com, shakeel.butt@linux.dev, kernel-team@meta.com References: <20260921153108.2713179-1-usama.arif@linux.dev> Content-Language: en-US From: Sandipan Das In-Reply-To: <20260921153108.2713179-1-usama.arif@linux.dev> Content-Type: text/plain; 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Both searches are redundant. > > Neither callback is normally hot. That changes once more events target > a PMU than it has counters. Perf then multiplexes them: every mux tick > deschedules the resident set and schedules the next one, so both callbacks > run for each rotated event on every tick. > > Meta's fleet-wide profiles attribute 1.1% of kernel CPU time, excluding > do_idle(), to amd_uncore_add() and amd_uncore_del() combined. On the > host that exposed this, a workload holding 15,782 perf event file > descriptors drove 56,575 calls per second into each callback from mux > rotation, against a 16-counter DF PMU. > > Patch 1 removes the scan in amd_uncore_add(). It walks every counter > before the free slot search, which is the common case once multiplexing > has scheduled the event out. > > Patch 2 makes amd_uncore_del() free the recorded slot directly instead > of rescanning from slot zero. Deleting all events from a full PMU with > N counters drops from N * (N + 1) / 2 compare-exchanges to N. > > No functional change intended. > > Usama Arif (2): > perf/x86/amd/uncore: Remove redundant event slot scan > perf/x86/amd/uncore: Free counter slot by index > > arch/x86/events/amd/uncore.c | 24 +++++++++--------------- > 1 file changed, 9 insertions(+), 15 deletions(-) > For the series Reviewed-by: Sandipan Das