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[149.14.88.26]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4771e202093sm43202745e9.11.2025.10.29.03.26.40 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 29 Oct 2025 03:26:41 -0700 (PDT) Message-ID: Date: Wed, 29 Oct 2025 11:26:39 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 0/3] Optimize code generation during context To: Xie Yuanbin , riel@surriel.com, linux@armlinux.org.uk, mathieu.desnoyers@efficios.com, paulmck@kernel.org, pjw@kernel.org, palmer@dabbelt.com, aou@eecs.berkeley.edu, alex@ghiti.fr, hca@linux.ibm.com, gor@linux.ibm.com, agordeev@linux.ibm.com, borntraeger@linux.ibm.com, svens@linux.ibm.com, davem@davemloft.net, andreas@gaisler.com, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, luto@kernel.org, peterz@infradead.org, 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, anna-maria@linutronix.de, frederic@kernel.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, thuth@redhat.com, akpm@linux-foundation.org, lorenzo.stoakes@oracle.com, segher@kernel.crashing.org, ryan.roberts@arm.com, max.kellermann@ionos.com, urezki@gmail.com, nysal@linux.ibm.com Cc: x86@kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, sparclinux@vger.kernel.org, linux-perf-users@vger.kernel.org, will@kernel.org References: <18734a4944e47952b7ad3e10a36c902392bdaa91.camel@surriel.com> <20251025173700.754-1-qq570070308@gmail.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset="us-ascii"; Format="flowed" Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org On 25.10.25 19:37, Xie Yuanbin wrote: > On Fri, 24 Oct 2025 17:36:06 -0400, Rik van Riel wrote: >> Also, what kind of performance improvement >> have you measured with these changes? > > When I debugged performance issues before, I used the company's equipment. > I could only observe the macro business performance data, but not the > specific scheduling time. Today I did some testing using my devices, > and the testing logic is as follows: > ``` > - return finish_task_switch(prev); > + start_time = rdtsc(); > + barrier(); > + rq = finish_task_switch(prev); > + barrier(); > + end_time = rdtsc; > + return rq; > ``` > > The test data is as follows: > 1. mitigations Off, without patches: 13.5 - 13.7 > 2. mitigations Off, with patches: 13.5 - 13.7 > 3. mitigations On, without patches: 23.3 - 23.6 > 4. mitigations On, with patches: 16.6 - 16.8 Such numbers absolutely have to be part of the relevant patches / cover letter to show that the compiler is not actually smart enough to make a good decision. Having that said, sometimes it helps to understand "why" the compiler does a bad job, and try to tackle that instead. For example, compilers will not inline functions that might be too big (there is a compiler tunable), factoring out slow-paths etc could help to convince the compiler to do the right thing. Of course, it's not always possible, and sometimes we just now that we always want to inline. -- Cheers David / dhildenb _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv