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Mon, 10 Feb 2020 18:53:20 +0000 From: Song Liu To: Kim Phillips CC: Arnaldo Carvalho de Melo , Peter Zijlstra , Ingo Molnar , Mark Rutland , Alexander Shishkin , Jiri Olsa , "Namhyung Kim" , Cong Wang , Jin Yao , Kan Liang , "Davidlohr Bueso" , "linux-perf-users@vger.kernel.org" , "linux-kernel@vger.kernel.org" , Jiri Olsa , Andi Kleen Subject: Re: [PATCH 1/3 v2] perf stat: don't report a null stalled cycles per insn metric Thread-Topic: [PATCH 1/3 v2] perf stat: don't report a null stalled cycles per insn metric Thread-Index: AQHV3gtC4rVViboGVU++YBPq+UJJxqgUyqIA Date: Mon, 10 Feb 2020 18:53:20 +0000 Message-ID: References: <20200207230613.26709-1-kim.phillips@amd.com> In-Reply-To: <20200207230613.26709-1-kim.phillips@amd.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-mailer: Apple Mail (2.3608.40.2.2.4) x-originating-ip: [2620:10d:c090:200::6281] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: 4365550d-43bd-416e-69d3-08d7ae5a7fa3 x-ms-traffictypediagnostic: BYAPR15MB3287: x-microsoft-antispam-prvs: x-fb-source: Internal x-ms-oob-tlc-oobclassifiers: OLM:9508; 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charset="us-ascii" Content-ID: Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-Network-Message-Id: 4365550d-43bd-416e-69d3-08d7ae5a7fa3 X-MS-Exchange-CrossTenant-originalarrivaltime: 10 Feb 2020 18:53:20.6730 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 8ae927fe-1255-47a7-a2af-5f3a069daaa2 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: LDXo8CR7a6j1/X6ycVObkxDozTnqm3+MpmPHB8RkBwCCv57fulw+yd8ABCEkys7MuT1rIutHG/PQWSLXLR+byQ== X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR15MB3287 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.138,18.0.572 definitions=2020-02-10_06:2020-02-10,2020-02-10 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 malwarescore=0 suspectscore=0 impostorscore=0 mlxlogscore=999 phishscore=0 bulkscore=0 priorityscore=1501 mlxscore=0 lowpriorityscore=0 spamscore=0 adultscore=0 clxscore=1015 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2001150001 definitions=main-2002100138 X-FB-Internal: deliver Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Feb 7, 2020, at 3:06 PM, Kim Phillips wrote: >=20 > For data collected on machines with front end stalled cycles supported, > such as found on modern AMD CPU families, commit 146540fb545b ("perf > stat: Always separate stalled cycles per insn") introduces a new line > in CSV output with a leading comma that upsets some automated scripts. > Scripts have to use "-e ex_ret_instr" to work around this issue, after > upgrading to a version of perf with that commit. >=20 > We could add "if (have_frontend_stalled && !config->csv_sep)" > to the not (total && avg) else clause, to emphasize that CSV users > are usually scripts, and are written to do only what is needed, i.e., > they wouldn't typically invoke "perf stat" without specifying an > explicit event list. >=20 > But - let alone CSV output - why should users now tolerate a constant > 0-reporting extra line in regular terminal output?: >=20 > BEFORE: >=20 > $ sudo perf stat --all-cpus -einstructions,cycles -- sleep 1 >=20 > Performance counter stats for 'system wide': >=20 > 181,110,981 instructions # 0.58 insn per cycl= e > # 0.00 stalled cycle= s per insn > 309,876,469 cycles >=20 > 1.002202582 seconds time elapsed >=20 > The user would not like to see the now permanent > "0.00 stalled cycles per insn" line fixture, as it gives > no useful information. >=20 > So this patch removes the printing of the zeroed stalled cycles > line altogether, almost reverting the very original commit fb4605ba47e7 > ("perf stat: Check for frontend stalled for metrics"), which seems > like it was written to normalize --metric-only column output > of common Intel machines at the time: modern Intel machines > have ceased to support the genericised frontend stalled metrics AFAICT. >=20 > AFTER: >=20 > $ sudo perf stat --all-cpus -einstructions,cycles -- sleep 1 >=20 > Performance counter stats for 'system wide': >=20 > 244,071,432 instructions # 0.69 insn per cycl= e > 355,353,490 cycles >=20 > 1.001862516 seconds time elapsed >=20 > Output behaviour when stalled cycles is indeed measured is not affected > (BEFORE =3D=3D AFTER): >=20 > $ sudo perf stat --all-cpus -einstructions,cycles,stalled-cycles-frontend= -- sleep 1 >=20 > Performance counter stats for 'system wide': >=20 > 247,227,799 instructions # 0.63 insn per cycl= e > # 0.26 stalled cycle= s per insn > 394,745,636 cycles > 63,194,485 stalled-cycles-frontend # 16.01% frontend cycl= es idle >=20 > 1.002079770 seconds time elapsed >=20 > Cc: Peter Zijlstra > Cc: Ingo Molnar > Cc: Arnaldo Carvalho de Melo > Cc: Mark Rutland > Cc: Alexander Shishkin > Cc: Jiri Olsa > Cc: Namhyung Kim > Cc: Cong Wang > Cc: Jin Yao > Cc: Kan Liang > Cc: Kim Phillips > Cc: Song Liu > Cc: Davidlohr Bueso > Cc: linux-perf-users@vger.kernel.org > Cc: linux-kernel@vger.kernel.org > Acked-by: Jiri Olsa > Acked-by: Andi Kleen > Fixes: 146540fb545b ("perf stat: Always separate stalled cycles per insn"= ) > Signed-off-by: Kim Phillips Acked-by: Song Liu Thanks for improving perf on AMD systems! =