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Thu, 19 Mar 2026 08:02:59 +0000 (GMT) Message-ID: <5e2f413d-2b09-4d27-9ab2-7936c91fc52d@linux.ibm.com> Date: Thu, 19 Mar 2026 09:02:59 +0100 Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v8 0/5] perf evsel fallback changes, better s390 defaults To: Ian Rogers , acme@kernel.org, namhyung@kernel.org Cc: agordeev@linux.ibm.com, gor@linux.ibm.com, hca@linux.ibm.com, japo@linux.ibm.com, linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, linux-s390@vger.kernel.org, sumanthk@linux.ibm.com References: <20260318175808.582009-1-irogers@google.com> <20260318234600.730340-1-irogers@google.com> Content-Language: en-US From: Thomas Richter Organization: IBM In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMzE5MDA1OSBTYWx0ZWRfX7/3ze4TfUfg2 wqTXw+etkCuv6pGTb4CedZTLxiuRUCyDdKkLxJZZBvLXN3ODiJd4X8owFVEXviYCv2B4tdpSTsV eDVGtJYpQ6aQicmGgEHImXRPt+ZzTcj+fRPw2p842Nink9M/TAEHFpKpafIkHOlIz1sRxi51Tfl Laoigc5R6rPSTUV517meS9f7T7rYl9L+UiCilr7jzUTztZy5LS8zotcORDpC0AGDVFD7t9+/MEU BWSuX7Qrn8P25I136jdUZjHVzxUEBzlCB/RkkN1EZFrWA8dxANf6g+zNHUyYJxMJfaubMTnyaFy w9kUYknOt7/7eETUmn+0TmdBPjl8Cmw72GhfjHQxb5M+DZz5s5hXs63L3WwhvrTB34rc53ypeUx PDezNYkN67vgvti3WxICT/EqBxZeOCAbjYRaAaYgRfx46uokjqZ4H5v7IJZhIoq5AM37VcX1Q8j 8LxLTm/5q/iZX4QgAng== X-Authority-Analysis: v=2.4 cv=GIQF0+NK c=1 sm=1 tr=0 ts=69bbadb9 cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=IkcTkHD0fZMA:10 a=Yq5XynenixoA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=RzCfie-kr_QcCd8fBx8p:22 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=c92rfblmAAAA:8 a=1XWaLZrsAAAA:8 a=gxYhOCFLj5_Kw6bs89EA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 a=GvGzcOZaWPEFPQC_NcjD:22 X-Proofpoint-ORIG-GUID: 8soTQZDNh53nbBe9-D4EcEAvZz6DtjQq X-Proofpoint-GUID: d85SBiPiGl-LBljQPpZQmtKWofIYN0Gs X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-03-19_01,2026-03-17_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 priorityscore=1501 bulkscore=0 lowpriorityscore=0 malwarescore=0 phishscore=0 impostorscore=0 suspectscore=0 adultscore=0 clxscore=1015 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2603050001 definitions=main-2603190059 On 3/19/26 06:39, Ian Rogers wrote: > On Wed, Mar 18, 2026 at 4:46 PM Ian Rogers wrote: >> >> Discussion with Thomas Richter in: >> https://lore.kernel.org/lkml/20260306071002.2526085-1-tmricht@linux.ibm.com/ >> showed that the evsel__fallback wasn't working for s390. These patches >> avoid the problematic frame pointer callchain on s390 and fix >> evsel__fallback from a range of problems when falling back to a >> software event. I simulated failures when developing the patches but >> they are untested other than that. > > I think at this point I call it a day. Sashiko still has feedback that > could justify a v9: > https://sashiko.dev/#/patchset/20260318234600.730340-1-irogers%40google.com > Specifically: > 1) software PMUs may fail if sysfs isn't mounted. This isn't a real > problem as "software" is a "well known" PMU that we create even if > sysfs isn't mounted. I totally agree with you. Patch set 8 should be it. Honestly, if /sys (of sysfs) is not mounted, I guess perf tool is the least of the issues that arise. I believe this is now getting 'over-engineered'. > 2) the handling of callchain in .perfconfig files isn't right, but the > patches aren't making it any worse. I worry there could be several > more patches if I start fixing things wrong with .perfconfig. Correct, you can not fix everything in one patch set :-) > 3) the possibility to add another NULL check for safety exists, but > the code would already crash at the same point. > Apparently, the tendency of prompts to generate further refinements > instead of providing all the problems at once is a known limitation of > LLMs and the current prompting methods. > > Thanks, > Ian > my 2 cents.... -- Thomas Richter, Dept 3303, IBM s390 Linux Development, Boeblingen, Germany -- IBM Deutschland Research & Development GmbH Vorsitzender des Aufsichtsrats: Wolfgang Wendt Geschäftsführung: David Faller Sitz der Gesellschaft: Böblingen / Registergericht: Amtsgericht Stuttgart, HRB 243294